See if you have the University roll number then it would be different from college to college although affiliated by the same university because every college have a institution code which differs from college to college and this institution code is the index of the college at the university. So if you have the university roll number then you should keep a note of the roll number and do contact your college officials because its not usual that you didn't have the registration number. Ask your officials either you have not collected it or you are getting it confused as roll number.

I hope this answer helps. All the very best for your future endeavors!