Sometimes, different embroidery threads shrink when washed. This 'bubbles' the embroidery work. I found that the closer I quilted the less it shows. The other thing I do with embroidered quilts is to have it dry cleaned. I know both of these things are a bit late for your quilt. I would try to press it some and stretch while pressing. You may still be able to quilt the block closer since it is only a single block. Others may have better ideas to help out.