White boards are amazingly useful surfaces on which you can write and draw over and over again. All you have to do is wipe the board clean between uses. Although white boards can become ruined if scratched or marred, restoring the board by repairing it yourself is possible.
Clean your white board thoroughly. Use your cloth and cleaning spray (any generic surface cleaner that's safe for plastic will do) or some water to wipe down all traces of marker and ink on the surface. Spray the cleaner or water over the board and wipe in circles, folding over the cloth when it gets dirty and constantly using clean material to wipe off more dirt and ink. If you don't, those traces will be embedded underneath your repairs.
Wait for the white board to dry. Lay it flat on the floor and then paint on a layer of white board coating. White board coating can be purchased online, but it can also be found at hobby and home improvement stores. Use a paintbrush and put a single layer of the surface over the white board. Allow at least an hour and a half for the coating to dry completely.
Use a white board marker over the scratched area. The coating should fill in the scratch, making the area smooth and once more able to be written on. Erase the mark and set the white board back on its frame.
If a single layer of coating isn't enough, you can apply a second coat once the first is dry.