Is your soil clay?
If your soil drains poorly because it is clay, mixing sand into the soil won't help. If it is a raised bed and you build a sandy bed above the clay, with compost, that could help.
Add soluble magnesium and/or calcium (as Epsom salts or gypsum) plus organic matter mixed into a clay soil to improve drainage. Anything high in sodium, mixed into clay, will make drainage worse.