It's been 6 days now and (not surprisingly)
it's still wet.

What do you mean, still wet? Do you mean "still green"? Dark greenish grey
color, not yet turning whitish grey?

Actually the slower concrete cures, the stronger it is. The interior will cure
at its own rate regardless, but if the outer skin (surface) is allowed to cure
too fast (dry out) it will crack. Curing compounds slow the evaporation of
water from the surface and prevent cracking due to differential shrinkage of
the surface compared to the interior. The best way to cure is to continually
wet the surface, but that's hard to maintain over a period of days.

I'm not familiar with the sealer you mentioned, but I don't think it will hurt
anything. Certainly, don't try to remove it. That would be asking for
problems. Give it some time and the concrete will turn a whitish grey. At
worst, you may need to apply the sealer again.
Gary Brady
Austin, TX