Imo getting to master by beating all levels on veteran is proving to be the hardest one.
Which one are you stuck on?
FInishing Arcade on Experienced without losing all ships. I've come very close on a few occasions, but since it takes a decent chunk of time (I don't game for more than an hour at a time these days) usually I'll give it only one shot per session.
Might have to do with the way I progressed through the game: by playing individual levels on increasing difficulty to keep my sessions short. I still haven't finished Mefitis on Master.
Update: Finally got the last Gold and the Platinum.