I'm sure you feel like your head is shaved, but really, you have a short haircut. It looks ok, but yes, you are thinning alot. I see no problem with your head shape, we are all our worse critics. I think every one of us was apprehensive before our first headshave.
That being said, you have been thinking about shaving your head for awhile. There is only one way to find out how it will look and if you like it. Of course you're asking a bunch of guys that like sporting a bald head, but to for the full headshave. If you don't like it, in a couple weeks you'll be back to a buzzcut.