Christina1234, please don't feel dumb. There could be several reasons why you have the same teacher. Often school principals move teachers around as they see fit or where there are openings. Sometimes the teacher wants to switch grade levels or subjects. This is normal.
If for some reason you don't get along with this teacher, I suggest talking to your parents. Then go in (with them if possible) to the guidance counselor to see if you can be moved to a different class. During this meeting state the facts. If you go in and asy I just don't like her or she doesn't like me, most likely nothing will be done. However, if you go in and present a strong argument, they might just make the switch.
Whether you've moved on to a new grade or you're repeating a grade, it's because your school administrators and teachers think it's best for you, right now. You'll have a chance to review anything that was particularly tough, and you'll have a head start on the concepts you'll be learning!
While I understand your frustration with the situation, I think you should prepare yourself for a less stressful and very enjoyable year! I also suggest that you talk to your parents, the teacher, or a school guidance counselor about your feelings.