I used to move my hoop around and it flatten some area. Washing the finish product will help but if you don't want to wash, just run your empty needle under those flattened stitches and they will spring back.
I now stitch without hoops or frames as I can take 2 stitches at once and it's faster that way. Admitted, the fabric tends to stretch diagonally slightly but pulling it straight during framing will take care of that.