You'd have to sand it down and get all the gesso off, then you can continue to cover it in oils. If it was an expensive canvas, I would not just throw it away. I am not the type to do such things. I mean, if it was one of those store-bought canvases, I don't know if it will even be strong enough to take the sanding. Those are usually like a 10 oz canvas, which are not super great, but maybe it's a 12 Oz. Was it from Blick? Maybe their canvases are better quality than I think they are.
Anyway, if you can, don't just toss out a canvas with oil paint on it into a land fill. give it a light sanding, get that gesso off of it, and make something beautiful on top.
Also, if the canvas gives and stretches after you sand it, you can always spray the back with water and it will dry tight again.