Seriously, if you want to exchange it, do it. Don't feel bad about it. You will be charged the restocking fee unfortunately. But the plastic MacBooks are just not worth the money.
You have to deal with that god forsaken Intel GMA X3100 GPU and the poorly built plastic case. I had two plastic MacBooks (one was a replacement) and they went out for repair nearly 8 times combined just because of the typical issues with the plastic. Cracking in various places, discoloration from heat and use. Its ridiculous. The plastic MacBooks are terrible. They finally replaced it with an aluminum MacBook. This thing is great. Just take it back and get the one you want.
The gift giver will understand. Plus if you explain the common problems with the plastic that you generally don't find out about until well after you've bought and owned the system for months, they'll be even more understanding. So just go get the aluminum one. The plastic systems are a complete waste of money.