Playing the 'flat keys' (F, Bb, Eb) on a fiddle are technically no more difficult than playing the 'sharp keys' (G, D, A). In fact, for some tunes, I think the flat keys sound better - better resonances I think. It's just a matter of playing the scales and tunes in flat keys enough so that your fingers become accustomed to them. So you should learn to do that, and you will have much more flexibility in what you can play.

Cheers, S. in Seattle