Many years ago a friend wanted me to make a confirmation dress for her daughter - when I priced it out for her (fabric, notions, my labor, etc.) she said "but I could buy one for less than that!" so I told her to go out and buy it. Understand that while you think the quilt is almost too simple, the customer asked you to make it because he couldn't do it himself. And he is willing to pay you for your skills and talent. Just because it was easy for you doesn't mean it would be easy for everyone else. You have expertise and how lucky that you have someone who understands that and wants to honor it with a tangible reward ($$$). So say thank you, don't feel guilty, the quilt is lovely and perfect for a new baby girl. And worth every penny he paid you.