If you are lucky, you just spilled some sand in the wrong place. If that's the problem, you shouldn't have sand CONTINUING to enter the pool.

If you are not so lucky -- and sand is continuing to enter the pool -- something went wrong during re-assembly. Two common problems are
(1) Failing to re-assemble the air bleed line correctly
(2) Cracking a lateral.

If you post exact make / model of your filter, someone may be able to give more specific advice.