Happens all the time. I find myself more comfortable vs protoss and zerg simply because I run into more of them when I play. When it comes to playing vs terran, it just seems that I don't have enough practice with all the timings and builds.

Plus it also happens at the pro level. Casy has some fucking top notch TvZ and some decent TvT, but god he is soooooooo bad at TvP. I swear he plays at like C+ level.