Star baby quilt top - with a slight problem

A few weeks ago (actually, a few weeks before Thanksgiving) I was feeling like I had done a lot of apparel sewing this year and not enough quilting.  I have fabric and pattern all ready to go for two or three lap to bed size quilts, but I was also feeling kind of overwhelmed with work and job-searching (I'm expecting to graduate in May), so I pulled out a Simply Color charm pack I've had sitting around for a while and the leftover grey background fabric from my Half Moon Modern Half-Square Triangle quilt and went to town with this free Moda pattern.

It took two evenings to piece the top.  I didn't trim my HST units or pin any seams until I had all of the rows sewn together.  It was quick and easy and fun, and really satisfying to get it done quickly, and I think it looks great - but it is decidedly not flat, which I'm feeling pretty okay about.  I think it will quilt out just fine.  I am not stressing out about this little baby quilt.

The problem came at the end of the second night of piecing, when I pulled out the fabric I had bought for backing and binding when I bought the charm pack.  I only have one yard of the backing fabric.  Lately I've been in a groove of making baby quilts about 40" by 50" and so I assumed that I would have 1.5 yards for the backing, but I don't.  I don't have enough binding fabric to do anything but bind it (only 1/3 yard!) and I don't have any of the grey fabric left over.  I think what I'm going to do is trim 4" of of the two wider borders on the top and then piece that fabric into the back along with a few leftover charm squares that didn't get used in the top.

I'm not really feeling inspired to finish this quilt right now, but at least I have a plan for how to finish it.  I don't like to have long-term hibernating UFOs, but I also don't know of any babies who will be needing a quilt from me any time soon, so I think I'm going to piece the back and then fold it all up until I feel like finishing it.