Mine vary widely. I've done 36 x 44", 42 x 55", 38 x 52", and the one I'm starting in January is 40 x 54".
I would probably add at least 2-4" to the sides in order to get it the right proportion, but that's just me. You definitely could keep it as is. Even at 34"W it will still be wider and longer than the baby.