Sticky spots or uncured resin

The cause is most likely due to not fully mixing the epoxy even if measured at the correct ratio or alternatively mixing epoxy that has not been measured at the correct ratio (or the weather is too cold to effect a cure). To remove, manually dig out all the sticky resin. Wash with aggressive solvents like acetone and when dry, grind or sand the surface to apply a second coat of epoxy. Curing of epoxy takes a lot longer in winter than in summer. In cold nights at below 10 deg C, the epoxy will stay wet for days until the temperature rises.