Howdoo Platty, welcome to the forum.
Check out some of the other recent threads here as regards the handling, probable that the geometry need setting but there are other things to check and consider first such as tyre pressures initially, then shocks, springs, wishbones etc.
As to performance, again, several things can restrict the car. Post up in the help sections and no doubt someone will assist where they can.
Also, the search facility, whilst not the bestest, can reveal some gems to get your car up and running better.
Post up your location and more car details when you get a chance. No doubt there is someone close who can give you a hands on assist if required.