I realize you are young and this is hard, but if the guy just blew you off you need to tell someone as soon as possible. You do not know if he is a predator or whatever. At best he is an insensitive jerk. At worst he could be a pedophile. Inappropriate behavior should not be tolerated by anyone. I would talk to the sensei. He/she is responsible for the school and is in charge on the mat. I would also make sure your parents know and, if necessary, take them with you to tell the sensei.