Didnt even know this was growing

I think its been growing for 2 months

I’m a full noob at this. A couple of months ago that planted a seed in a water bottle cut in half with holes at the bottom of it, I filled it with pine grow soil and watered it once and I didn’t know how to take care of it so I just tipped It out to try find the seed but I couldn’t find it so I I just left it there and for got about it then two months later I was going out two get lunch when my dad found this plant growing in the pot. He questioned me and asked if it was mine and I said I I didn’t know it was there at all and the weird thing is that I haven’t even watered it once since I tipped it out. It’s looking pretty healthy and I don’t want it to go to waste so someone please give me some tips on how to look after it please. Text me on Instagram: thomas._.sparrow