mystery plant/ 13 and 7 day old girls (with pics)

i do believe that we have an extra marijuana plant, although we never planted it. how would an extra plant get into our pot without us putting it there? should i remove it? our plants our too young yet to be producing seeds.
also, some of the leafs got burnt due to being too close to the light, it doesn't appear to have stunted growth, just singed the outside.

Originally Posted by lagarrettBLUNT

idk but remove those mystery plants you dont want them to interfere

i removed the plants, but the other 2 plants that were in with one of the mystery plants are still looking deficient and are growing slower than the rest. what should i do?