Yeah, I've had the same problem when trying to remove the last bit of activated charcoal from a liquid when only a coarse grade filter paper and celite was available--infact, in this case, you might be better off by just filtering the activated charcoal WITHOUT celite then letting it settle to the bottom. Sometimes using multiple coffee filters can help... but better yet is to use a finer-grade paper, like qualitative whatman's.
Btw, if you're saying your celite is SOLUBLE, then you most certainly not have celite... if you're saying it easily passes thru coarse grade paper, then you definitely have the right celite...
Btw, there's little use for activated charcoal if your NaGHB/GBL tastes right (i.e. normal lactone or salty taste).