Just another small hint...Once you've got them closer to the same length and ready to sew on your borders, put whichever is the fullest on the bottom when you sew. Typically your machine pulls the bottom fabric next to the feed dogs through a little faster. At least that's the way it seems to me.
doggone it, I forgot who posted this reply, oh, think it was bj, lol. just wanted to give you credit. Fons and Porter say you are right about this. Always sew with a baggy bottom, lol!