First, the quilting is wonderful! I agree that $50 is not enough, but you should have agreed on a price beforehand, so you are only going to get what you get. Most quilters charge by the square inch. You did custom quilting. The rate for custom quilting usually starts at $0.025 - $0.03 per square inch, so just the quilting would be around $65 to $80. Add in the binding charge that I would estimate at about $25, and you are up around $90 to $105.
Treat this as a learning experience, and don't take another quilting job unless the terms are agreed to (and written down!) before you start.