you're quite right showtime, but Superman's DNA was used to create Superboy as well. Bizzaro is a degenerate clone of Superman while Superboy is a partial clone. this could be explained easily: the DNA that Lex obtained was highly contaminated by the kryptonite shard that Lex used to stab Superman with, thereby creating Bizzaro (i know thats not how it happened in the comics but i'm just thinking in terms of the film universe for now) but Kryptonian DNA is similar enough to human DNA that human DNA could be grafted onto it in order to stabilize it and neutralize its degenerative nature, thereby creating Superboy.
the above situation would actually function as a separate Superboy spinoff movie now that i think about it (albeit the plot will have to be more developed but it could work). one of Superboy's "titles" in the comics was Project 13, so i guess Bizzaro could be the failed Project 12. i'm really just freewriting at this point lol but i'll stop now