IGETC is mainly to certify that you finished the lower division GEs, but transfers still wind up taking some additional class or two to fulfill reqs by whichever college you get placed into (I think ERC has a pretty tough writing sequence, Muir has an additional writing class, and Revelle has extra math & science classes you need to take on top of being IGETC certified).
I’m not sure exactly what you’re asking, though. Are you confused about whether or not you took the right courses for a STEM path?