Can I transition from 3 years out of school to a master's in computer science?
Sure it's possible and some small fraction of people have industry experience (or teaching experience or military service or what have you).  Has always been this way.  It's a minority but normal.  (Actually in good MBA programs its the expectation.  And in law and medicine its very normal, not as rare.  In research it's rare but just because of the population not going that way, not because of schools discouraging it.)

In terms of math prep, I donno.  Guess you should look at different programs and talk to them (good chance to talk about other things in general also).  Maybe there are programs where it matters more/less your math background. Maybe you can get some individual calibration on your specifics, which this forum sometimes discourages.

Finally, your title and then question text itself are a little confusing.  Are you asking about math requirements for CS MS (which would be an issue regardless of your interregnum) or for how the interregnum is looked at.