Piano Accompaniment

Being a piano accompanist for my sister's Suzuki group class is hard.

I don't feel particularly nervous, partially because I'm only in a supporting role, partially because the audience is very small, but I'm screwing up a lot, despite that. Not screwing up in playing wrong notes so much as just dropping out. I don't feel nervous, but I do feel inhibited, like sometimes my fingers don't want to continue playing a certain phrase. I'm inhibited because I don't want to screw up, but also because a lot of times the piano plays a different part from the violins. While I'm used to harmonizing with a group as a clarinet, the vast majority of my experience on the piano is as the melody AND harmony at the same time, rather than alternating. So, that fraction of a second where I realize that I'm not playing with the violins anymore is enough to make me drop out for several measures-- sometimes.

What can I do to fix this? Memorize the pieces I'm playing(1) , so I can focus on just one part, (the violins) instead of three parts at once. Other than that, just keep playing in my sister's group class on Mondays until I'm used to harmonizing with three or eight or a dozen violins.

1: and it's not like they are hard to memorize, just that there are so many of them.