GABA only lasts so long and it all depends on what the drug is taken for.
I take 1600/MG/day to an actual reason - seizure. I've been taking these along w/ Keppra for years and years, so I get no "feeling" from it all. but I do remember early on I would always have a happy-go-lucky smile on my face for a few hours but nothing out of the ordinary really. eventually, after about a month, it somewhat wore off but I still see post about GABA which I find so funny because I take it for an actual purpose and feel none of these effects, oh well.
if you continue w/ the FENT and the GABA the the GABA will surly fade; however, you mentioned you still had a full day of school. dude, you are young, so lay off this garbage now before it gets too damn late and god knows what could happen; mixing anything is a NO-NO, although these are not something you'll hear many bad stories about its also nothing something you hear great stories with either. just be careful w/ what you are doing and realize that FENT is bullshit and if anything stick w/ GABA and have an overall good time rather than just the 10-20 minutes the fent would give you.