Just stay in the gym. You know that there are the 5 different 3s the 2 wings, the 2 corners and the point so take 25 3s from each. Do some ball handling drills and shoot 100 free throws. I do this most days and it really helps me.
Go to youtube and watch the channel "BBALLBREAKDOWN". Most of their videos have some great tips on 3pt shooting. The Jeremy Lin and Anthony Davis videos I have found to be the most helpful. Practice them and you'll get a lot better in game situations. I went from about 10% 3-pointer makes to around 40% 3-pointer makes.
Message me at BasketballTrainingClub.com, and we'll get you some free shooting and ball handling drills, ok?