B.Sc

Yes, you can. You need to qualify the entrance test of the college in which you want to take admission. At the time of admission, you need to present the portfolio which you have prepared.

M.Sc is a better option, but I will advise you to opt for some other subject.

You can go for GRE/GMAT. These exam scores are taken by foreign universities for admission. Along with these exams you also need to clear TOFEL which is an language proficiency exam.

If you given the maths improvement exam in 2015 and got result in the same year, you must mention the passing year as 2015.

Sachin you can't opt for M.Tech after B.Sc, you need to have a B.Tech degree to pursue M.Tech or you must have cleared the AMIE examination.

The eligibility depends on the type of course that you wish to pursue, the details of some courses is stated below:
Diploma Class 10th pass from a recognised board with minimum 40% marks.
Bachelors Degree: Class 10+2 examination with at least 50% marks.
Post-graduation degree: Bachelors degree from a recognised university with at least 45% marks.
Graduate & PG programs may also require you to appear in entrance exams such as NCHMCT, AIMA UGAT, E-CHAT etc.

You can go for below courses-
M.Sc Mathematics
M.Sc Physics
M.Sc Chemistry
M.Sc Computers
M.Sc Zoology
M.Sc Botany
MBA
MCA
B.Ed

You should opt for BCA. BCA is a job oriented course.