Okay, it sounds like the Bangladesh system is very different and it's too bad that you cannot do any of the things that were suggested above, because I think any of those things would be better than what is suggested below.
1. Do you have any elective courses in your degree? Or do you have to follow a predetermined list of courses, with no choices? If you have electives, then take all of them from the Physics department if possible. Not just Physics related courses, but take courses taught by Physics professors with other Physics students. Your list of Physics courses sound like the courses engineers in Canada (and probably North America) would take, where you will learn some of the same Physics principles, which is good, but from talking to my engineer friends, the focus of these classes is very different from what one would expect from a Physics student. Also, the material seem to only cover the first two or so years of Physics material. So you will have to make up for the material covered in the later years of a Physics degree if you want to compete with North American and European physics majors. Here is an example of the courses a physics major might need to take:http://www.phas.ubc.ca/undergrad-honours-physics
-- note that there are more physics courses required, based on your interests. Read the notes on what physics electives are eligible and compare course numbers to this page: http://courses.phas.ubc.ca/Current/PHYS_list.phtml
I've linked to you an "Honours" degree track but that is what you would have to take in Canada to go into good grad schools. A "major" track can still get you into graduate programs but the difference is actually pretty small (fewer math classes, no senior thesis).
2. It seems like you will have the basic math requirements (compare to links above), except for dedicated Differential Equations course(s). Try to take them from your Math or Physics departments. Sometimes the Math department class might be more theoretical than necessary and your Physics department may offer a class that is more practical to Physics problems.
Also, if you are able to, you could supplement your math courses with a dedicated Vector Calculus course and a dedicated linear algebra course from your school's math department, if you don't feel prepared enough after your program's combined vector calculus/linear algebra course.
I guess my main concern is that all of your math are covered in just 3 classes while normally a North American student will take the same material over at least 6 courses. Maybe the school semesters are much longer though. In Canada, each course is 12-13 weeks and in the US, they are sometimes 10 weeks (quarter) or 16 weeks (semester).
(If you cannot take any of these classes at your school, then I guess taking them online will be better than nothing. But these courses aren't usually accepted as substitutes. At the very least, they will allow you to learn about your interest in Physics!)
3. Research. You should try to get research experience, in Physics if possible, during the summers of your program. Definitely at least do an thesis project in Physics if possible. If your school does not offer Physics research, you should know that some other schools in the US and Europe have awards that you can compete for to get international research work during the summers.