Are you keeping it closed? I can see where it would help the mind focus on a point but I've always found that in all shooting (bow, rifle, pistol, shotgun) I do better if both eyes are open...HOWEVER...there've been several times I find squinting lightly and FORCING my dominant eye to be, well, *dominant* helps.
You lose depth-perception when you close one eye...so be mindful to not train yourself to close your eye before your brain can judge the distance.