While what you are dealing with certainly needs examination and an answer as to what it is, I think you can rule out an oral squamous cell carcinoma. The youngest person I have ever read or heard of that has had one was in their late teens. I just did a Medline search and found no reported cases in children in the literature. Hopefully you will find this to be something easily treatable and not serious. While I have not searched every medical database, I hope that this posting gives you some peace of mind till your appointment. When you visit the doctor, have him consider various forms of epulis ganulomas or fibromas in his differential diagnosis. These things are all benign, occur in children the age you have described, and from your description MAY be worth consideration. As you are no doubt aware, from a description over the web it would be difficult for anyone to diagnose exactly what this may be.