By spray glue, do you mean basting spray? Like 505? I don't think basting spray would shrink a queen-size backing by more than 4". My best guess is that your measurements were a bit off. Adding 2" all around means everything needs to measure 4 inches bigger in width and length.
If it's just one side that's short, I would *carefully* sew an extra strip of backing fabric on. If it's a print fabric, likely no one but you will ever notice. The biggest problem is that the basting sprayed side of the fabric will be tacky. You will be sewing fabric right sides together. I would sew with the tacky side up and lay a sheet of typing paper over the tackiness so it will slide under the machine foot. You can sew right through the paper, then remove the paper from both sides of the sewn seam.