Does your cat pee on other things? This is a behavioral issue. Cats are very territorial. I had a spayed female who marked everything in the house, including my piano. She had to be banished from the house except for the family room. I had her for 21 years.
I hope you can get enough of the odor out that you can finish then wash the quilt. It looks like a beautiful quilt.
Cats will go back to the same place and repeat the act. So beware.
Cynthia