Pull it out, look at it.It may not be as bad as you fear.I recently did this,and was surprised how well it actually looks,now it is in the pile to quilt the next few months. If it is looking kind iffy, or even a twinge of negative emotion starts,then use the UFO in other ways,section it out for pet beds(if you have pets), pillow tops/blankies for future grandchild, even tension/bobbin setting practice cloths, or put it in the goodwill bin for some other quilter to find it to work with. Only you can decide on this, but what ever the decision, keep you in mind that it will be for you to do in a positive step,not ever a negative one. Frustration, guilt, ect. are very negative and your life, and the time you have with it, is more valuable than a UFO. And yes, I get that you have a sentimental attachment to this project because of the material being from curtains you made for son's room, but I bet you didn't keep every stitch of clothing you got him throughout his years growing up either.LOL!Though I know if you are like me, you kept somethings(my son is late 30's and I kept some,to include is graduation gown... Seriously, good luck in any decision you make.