I don't hear anything wrong with the mixing/mastering, don't fret :)
This is experimental in a really cool way, definitely reminds me a lot of games I played in the 90's on Sega Genesis. Did you play the guitar solo on a guitar?
If you're working in FL Studio as the software list shows, Maximus is a really good single VST for the master bus, it's about all the mastering I use when I am in FL. Anyway, solid work, sounds great!