Pay close attention to how you nock your arrows.

9 times out of 10 (assuming you have a semi-decent string and your pro served the peep in with the twists and not againest them), peep rotation is caused by nocking the arrow to the side of square with the rest and then rotating the arrow over to the rest. Whisker Biscuit users are the most common offenders, but dang near everyone does it... and just doesn't think about it.

Of course, as you said, it is a new bow... so your string is going to stretch and settle a bit. I'd shoot it a few times at the pro shop until it stops moving. Even if it is crooked, at least it is repeatable. Then have him adjust it accordingly. Good luck.