That is a nice tomato plant! I think you should keep it. Just don't water it quite so much, and it wants a bit of plant food, mixed up weak. As a bonus, tomato plants are EXCELLENT for hiding cannabis plants if you put them very close together. You can even hang little red-painted Christmas tree balls on them so they look even MORE like a big bunch of tomato bushes! Starting your tomatoes before your pot is a good idea, so the tomatoes have a chance to get big for the pot to hide behind. I have seen some growers plant one of each species in the same tomato cage, and pictures taken from more than a few feet away show nothing but a vegetable patch!

Every potted plant, of any species, that you grow is one step closer to becoming a great ganja farmer. Keep it up, and try a new set of seeds... perhaps from an actual baggie of weed so you are 100% certain that they are pot.
And never re-use soil, because you can get straggler seeds from whatever had been in there before. I bet that's what happened.

There's a link in my siggy about basic growing that will get you a bit further down the road.