Can I spot-fix or polish uneven epoxy, or do I have to repour everything?

You don't need to strip the epoxy off and start over. Cured epoxy can be sanded and re-coated, and the new flood coat cures clear and glass-like again as long as correct mixing procedures are followed.

Wait at least 12 hours after the pour so the epoxy is hard enough to sand. Sand out the imperfections (high spots, drips, ripples, gritty texture) with whatever grit you prefer, then finish by sanding the entire surface, including the sides, with 220–320 grit. If the whole top is gritty, sand the full epoxy layer with the same grit. Wipe the dust off with a clean, lint-free rag and denatured alcohol or acetone, let it dry completely, and pour a new full flood coat. The new coat fills in the sanding scratches.

Don't sand through to bare wood. If you expose wood, seal coat it again (once or more) before the flood coat, or air bubbles will rise into the new pour.

Spot fixing is possible: sand the spot, clean it with acetone, and brush epoxy over that area. But it leaves a visible seam where new epoxy meets old, and results vary. A full flood coat over the entire surface is the only way to get a seamless finish.

Polishing sanded epoxy back to gloss is tricky and takes practice, so we recommend re-pouring instead. And the flood coat can't be rolled on thin or spread out; it has to be poured at its full 1/8" thickness to self-level and cure properly.