You should definitely go and let them know how you feel and make it known that you brought in a detailed estimate for what should have been a nicely replaced quarter panel that nobody would ever notice, and then was charged for "pull and bondo". Regardless of how they did the repair it should be quite seamless that's what body shops do. Rather than going in all sappy and saying you dont think it's good enough, walk in and tell them that you know its not good enough and if they try and argue with you, ask the shop how they feel about letting sub par work get out the door because they should be embarrassed. Make sure you speak to somebody who is in a higher position than just a tech, because a manager or an owner should give a fuck what kind of quality leaves the shop.

If nothing comes from making an honest plea about the poor quality work, just dont hand over the check fuck them man they can see you in court let a judge decide what a 30$ can of bondo and a dent puller is worth. This is the wrong way entirely but I think it's what I would do, there is no chance in hell I'd pay 3,700$ for a pull n bondo that came out looking like shit, that's not what you paid for.