I have a lump on my back the size of half a football do limpoma s grow that big? It starts just below my shoulder blade and curves to my side

See your doctor. Lipomas can get very large. Lipomas can be removed. See a surgeon to evaluate for excision.
SEE SOMEONE. Lipomas can get large and are very characteristically soft feeling. That one sounds quite large and can cause you some irritation. Go get it checked out and removed before it gets larger.