Your question is not educational, but I'll be happy to give you some advice.
From a person who has dealt with a parent comparing me to others, I completely understand how you feel. Parents do sometimes get mad at their children for misbehaving but it not acceptable whatsoever to bring them down like that. I hope you understand that no one but YOU is allowed to dictate your worth. If you can, I suggest bringing this matter up with your mother and tell her how her remarks make you feel. If you cannot do that, I suggest speaking with a school counselor, friend, relative, or teacher about this. Sometimes expressing your feelings with others is the best medicine.
Have a great day!