Potato plants grow to their containers. I'm surprised it is going straight up line that, but considering the size of the trashcan, it seems relatively normal. It may not flower, that's fine. They don't have to flower. Just keep waiting now. I'd advise against filing it all the way up with dirt, just because it might take that add a signal to get taller still. But the can should be at least 3/4th full of dirt.