It's OK, except there is a very high probability that you should have put "did" instead of "made".

I would have said "I was procrastinating instead of studying math, and I made something cool." I don't know why people are saying your sentence us grammatically ok, because I've never seen the word procrastinating used with another verb like that.

It's grammatically ok, but the two halves of the sentence don't seem to have any relationship to each other.

“I procrastinated studying my math, so I made something else cool instead”.