A bike should track straight with your hands off the bars on a level road. The headset may need adjustment, or a wheel may be out of true, or simply not well centered.
Take the bike to the shop, and ask to talk with the manager. Explain the problem. Most good shops will take the time to get the bike exactly right. If THIS shop refuses, take the bike to a better shop to get the work done. And, of course, make your future purchases from that better shop.