Like Stick said, shim it. You don't want to use anything you can't separate easily when the time comes. I also recommend taking the wax ring and throw it in the garbage or use it in the shop as someone suggested a while back for lubing screws to make them easier to drive. Buy a higher tech unit (about $15) to seal with. Some are reusable, if you had to replace flooring for example, and there is absolutely no way that some of them can leak. The best one I've seen made a surface seal against the pipe flange and also had a rubber nipple that went down the inside of the pipe about 2 inches or so and sealed against the wall of the pipe. It was impossible for that setup to leak unless the rubber disintegrated over time.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.