But I have an offer in the regular BE degree...
well then, you can't take that particular Diploma
Engineering already has a lot of Maths as it is, either separate ones (like Calculus and Linear Algebra - both of these are common to all Engg students) or integrated into Engineering subjects - I know this for a fact, since I tried to get an Engineering subject as an elective for this year but I wasn't able to since at least one 1st year maths, which I didn't take, was a prerequisite
Besides, it's an unaccepted fact (well, at least I reckon so anyway) that if you're in Engineering, you ARE supposed to be good at Maths so it's a bit of a redundancy if you still seek to have a separate Maths qualification.
Oh, and it's not only Electrical Engg that is really associated with Maths. Cvil Engg, among everything else, also has lots (plus Physics) - can you imagine what would happen if bridges were built without engineers bothering about mathematical calculations?