Hi Alison,
Too Much Fun paints are (in my opinion) the thinnest on the market for airbrushing. The problem is probably with your airbrush - I have two of the Olympos HP-8 and hate them! I get all sorts of problems with them so I ust use my Iwata HP-B or Badger 100SG - both these airbrushes are wonderful.
The Olympos is sold by Too Much Fun specifically for nail art, but I just find it too fiddly. If you can, change your airbrush (preferably to the Iwata) and you'll see a huge difference.
Have you had training or are you just trying to teach yourself? I can't stress enough how important it is to get some proper training, if you don't and continue with the problems, your equipment will probably end up in a corner somewhere not being used, which would be such a waste. :cry: