The stickiness can occur for 3 reasons with the GiGi sealer;
1. if parts A and B are not mixed thoroughly during the mixing process
2. if too much sealer is left on after each coat
3. the sealer has not cured completely due to low temperature
If it is really sticky or tacky then this can be removed using acetone. You can then reapply the last coat of sealer using the standard method.
Further tips are;
Use a mechanical mixer such as an electric kitchen whisk.
Increase the temperature of the room and/or concrete by dialing up the central heating if indoors or using electric blankets if outdoors