^^^Cosign.
I will say that since you signed splitsheets and got $1200 upfront, everything seems in place. I'll be honest, I've signed off on tons of stuff without lawyers present, but I'm usually pretty good at understanding contracts. As long as everything is in reference to just one piece of work, I've never cared much, I can make more songs and get more checks. I'd take the 1200 and whatever splits I agreed to, and keep it moving for relationship purposes. I'd stay in contact, continue sending music, watch the artist's progression, and if my song made him rich, I'd know to charge more for the next song of mine that he uses. I'd also keep in touch with the label, if this song does good, you're in the race as a good developmental musician, they will bring more new talent to you to create songs.
You can screw alot of that up by voiding your original agreement. That's not saying not to meet with a lawyer, that's saying that if you got cheated out of hundreds of dollars, even a few thousand, it may not be worth screwing the opportunity and relationship. It would be different if you never agreed in the 1st place, but trying to adjust now could just make them say "forget it, we won't use your song, give us back our upfront and never contact us again".
Not worth it.