I did this exact same thing with my first bag I made (different pattern). It was a larger bag so I just sewed it up on the three sides to make it look like a regular tote. It looks rather terrible because I also messed up on a few other things, but I just chalked it up to a learning experience. I still use it to carry books in or other items here and there. It doesn't look too bad from the outside and I seem to be the only one that notices. Sorry, I hope you can fix yours, but you need to pull out the quilted stitching and separate the lining from the outside.