Just for comparison sake, do you know how much sand your filter holds? Mine is rated for 325# and my starting pressure is ~20 psi.

You're only supposed to add enough DE for a ~1 psi pressure increase. I overshot mine also, but I found that if you shut the pump down for a few minutes and re-start the pressure somehow will come down. Mine went up to 26 on roughly one solo-size cup, but after I let it set for ~5 minutes it was back down to ~21 psi.