Like Purple said, try a different brand.
Back when I rode a motorcycle I went thru 5 helmets before I found one that fit perfectly. Each brand seems to have a slightly different shape. I found Bell and Shoei to be too narrow for my head and ended up with an Arai that I loved.
You might want to find a good motorcycle shop near you. They typically stock a decent collection of helmets and you can try them on. Also, don't be afraid to take it home and sit on the couch in it a bit to make sure you like it.
For the track it might be a little less critical than on a bike given the length a wear, etc, but it's still important that your helmet fit properly.
Don't feel like you need to spend $800, but also don't cheap out.