Sand alone for a plant tank is not the best idea, unless you plan to keep plants that are water column feeders!
The substrate is inert and it is best to add something to it. You are not that far along yet and perhaps just buy some flourite and redo the tank over a weekend or something.
You will be pleased you did. Let me just say that you can eventually make the sand rich, with mulm buildup and adding fertiliser directly to the sand. However plant tanks can get complicated enough without adding any aggrevation.