A couple of things:
If you sand, make sure the Future is fully cured—wait at least 48 hours. If it's gumming up the sand paper, wait longer or force cure.
Another option, if you have a good, light hand, is to brush paint over the sags with 90% isopropyl alcohol. You may be able to blend them in invisibly. I've done it, but you have to be careful not to have the brush too wet, and wait several hours between applications. The advantage is that you don't need to recoat. The disadvantage is that too much alcohol will ruin the paint job.
Good luck!