Hooray! Apparently the problems I was having were due to a) a broken darning foot, b) a wrong size of bobbin, and c) a misplaced needle. So I was lucky enough to drop it off yesterday and get it back today. I've tested out some free motion quilting on a small quilt sandwich (I didn't want to risk messing up on my quilt again) and so far so good!
Tomorrow is going to be a good quilting day.