To be honest, depending on what model of RX-7 you bought, it's not the car's fault that you're struggling, but the "Biological Interface"'s fault.
You should practice more on your driving and racing skills. 👍
There is
no substitute for learning the tracks.
Every bend, hairpin, kink and curve.
When you can run clean laps you'll find it's pretty easy to progress.
An unmodified RX-7 (FC) should easily obliterate the competition in the Sunday Cup and FR Challenge events in Beginner Hall without any difficulty at all, which should earn a little cash for you and 2 prize cars.
It should also do pretty well against the Renault 5 Turbo in the Easy Tarmac Rallies in Special Conditions hall which'll also earn cash and prize cars.
You might have to modify it slightly to compete with the cars in the Group "RE" event in the Mazda manufacturers specific races though.
An RX-7 (FD) should make things even easier.