Yes, likely letters are quite definite, but there is always a tiny chance something could happen: you could bomb a class, or a teacher could wreak havoc with one of your grades, etc. So I, too, suggest you apply to a few others to have as backups.
Also, is there any chance you could be caught drinking underage, DUI, or in posession of other illegal substances? Be very careful if you want the likely letter to survive your counselor's Mid Year and Final Reports.
Congratulations on being recruited, but it is good to keep in mind that the process can change from week to week if the coach is courting other prospects. He/she will be reranking the recruits as time goes by. Be sure to have other schools and other coaches ready to take you if P'ton changes their mind. Best of luck.