The good news is you almost certainly don't have to return the bike. The bad news is that (1) your bike isn't completely fitted to you, and (2) it isn't always super easy to figure out how to fit it.

You have too much weight on your hands. Saddle position is the most likely culprit, probably it's too far forward. After you work through that, you might want to raise the bars a hair, and/or rotate them back. It's not as likely, but your brifter might just be a bad match for your hands.