If you have forgotten your username, you can use the self-service tools on the MyDMV homepage.
on a somewhat related note, I will be moving with my girlfriend to her apartment, is there a time limit to declare my change of residence?
You must report a change of residence address on your license, permit, non-driver ID, or vehicle registration to the DMV within 10 days.
I'm still unable to complete the registration process because I've forgotten my temporary password. So, what do I do now?