The problem is not with you, it is with your teacher. You cannot possibly achieve your personal best without corrections from your teacher because it is through corrections that we learn. If the teacher is only focusing on the easy students you are not getting your money's worth, and you are left feeling the way you do. If I had a daughter in your position I would immediately start looking for a better school, one with a focus on ballet rather than a lot of different genres, and especially one which didn't do competitions as they are known for very poor ballet technique. If you cannot change schools all that is left for you is to have a private talk with your teacher (your parents should be involved in this) and tell her you need her attention and especially corrections in class. Your part in this cooperation is to implement her corrections immediately (it helps to keep a notebook in your dance bag and write the corrections in it for reference). I hope, though, that you will find a better school.
As Mintchips has said, stop practicing at home. What will be beneficial is to take up Pilates, a common cross training practice of students on the professional track and professional dancers as well. If you are good at following directions you can find videos at your local library.
Good luck with this-- you owe it to yourself if you want to achieve the best possible.