Something is growing next to my plant

Hi, I don't know what it is, but what I do know is that you should remove it NOW! You can't have two plants in the same pot; they fight for resources and in the end, both produce very little. I think you should carefully take it out and put it in another pot to see what it is. I don't know if you've had more seeds and one might have fallen, another question is this: cheap substrates often come with seeds that germinate, and they can obviously be seeds of anything. Cheers!