​There is no easy answer to your situation.  You sound like you are capable of studying science.  But you are not interested in it.  Did you used to be interested and you lost your interest?  Or, you are someone who is not really interested in any subject, but can study well anyway.  I would say it is not possible to guide what is a good solution until we have more information on what you ARE interested in, not only that you are NOT INTERESTED in science.  If you don’t study science, what will you study?
I might be giving you the oldest philosophical advice when I say “Know yourself.”  If you do not know your interests and skills, you cannot give a good direction to your life.  And if you cannot give that direction, someone else will!    So, you can to give attention to the process of learning about yourself, not just about subject they teach in school.
At Insight, we advise students a simple model of self-discovery: reflect >engage >repeat. Reflect on your interests, what makes you happy, when have you been touched by an intense emotion?  You can , ask your parents, your friends, your siblings about their thoughts.  But reflection is not enough, you must get out of your head and enter the world.  Engage in some activity that you are interested in.  Really take part and to discover how you feel.  Did your interest increase or wane?  Now, you are reflecting.   This back and forth between action and reflection will help you better understand yourself.
Then, you would know what to do.  It is said, "Not having a plan, puts you at the mercy of those who do have one." If you know who you are, you will know what to do, and you will no longer be at the mercy of other people telling you what to do.

​This is not simple answer, but you may wish to pay attention to this answer. 
The myth is that if you study A Levels it’s easier to go get into colleges abroad. That is not the case at all and let me explain. If you get good grades in A Level for example 3 A's then yes, it would be easier. With the internationally renowned degree, every college will know that you are academically capable. But if you get 2 D's and an E, you are is worse off than getting 60% in Plus 2 because the colleges know that you are not academically capable. With a 60% in Plus 2, colleges would not really know how that measures up and your application will be reviewed with a benefit of doubt. 
In fact, I know lots of students, who have gotten full scholarships studying Plus 2 and lots of students who have not gotten into colleges abroad even though they have studied A Levels.  Does A Level help?  Yes, definitely, if you get good grades.  If you get bad grades, it can hurt.  If you are very sure you can do well in A Level, and yet you want to go abroad, you may be better off with a +2.
Yet, this is not a simple answer.  There is one more thing to consider. That is the study-culture.  Having said that, A Level is a superior program to Plus 2. With constantly updating syllabus, curriculum dealing with current world problems, the rigor involved to get you to think critically, A level does prepare you better for higher education. But an A Level does cost twice as much or sometimes much more in certain colleges in Nepal, than for Plus 2 program.  Let us say that two people get into a foreign college with equivalent grade, say Ramesh with D average in A Level and Divya with a 55% in +2.  Who is better off? Ramesh would have had exposure to international study culture, while Divya would not.  Ramesh is more likely to succeed in that case. 
So, if you ask – does A Level help in study abroad?  The answer is yes.  If you as – is A Level an advantage to go abroad?  The likely answer is a ‘no’ unless you are likely to get top grades.
According to KesharKhulal, Principal at Budhanilkantha School, "Plus 2 is the best options for students in Nepal, but A Level is better if you can afford it." 

​No. In fact computer classes and language classes can be useful.  But you should ask yourself are you really interested? Or are you going because your friends are going?
A lot of students take bridge courses after their SLC just because that is what everyone does. Parents are happy that their kids are 'studying'.  Bridge course institutes are happy that your parents are paying the fees, and you are happy as you feel you are not just sitting home doing nothing.  Many students do not take bridge courses seriously.  They mostly bunk those classes and go to the classes just to ‘kill time’ and to hang out with friends.  You don’t lose much by going, right?  After all, the course material in these courses will be parts that you have already studied or will naturally study later in high school.   So, you just go, what’s the harm?
If you are going just because everyone else is going, and you do not know if you are really interested in the course being taught, I would highly discourage you from joining bridge courses.   Sure, you need to prepare for what comes next in your life.  You should do research on your own, or with a group of friends.  All that is useful because you are an active learner in those classes.  In bridge courses, you just take in passively what is taught to you.  This may teach you a bad habit.
In conclusion, bridge courses are useful only if you have an active interest in the course.  If not, you are better of finding a more productive way of using your time.