You can buy flange extender rings to raise the top where it should be (if it can't be raised on its own). That is better than using two wax rings, less chance (not a huge one, but exists) of a blowout if you plunge the toilet. Test fit the toilet prior to final setting with the wax ring. If the toilet rocks after squishing the wax ring down, it doesn't bounce back and you'll have a failed ring. Shim the toilet so it is stable, remove, then install with the wax ring.