That depends on your future goals. If you want to study Medicine, then you should have a minimum aggregate of 50% in Physics, Chemistry and Biology or Biotechnology in your 12th. Then your 11th aggregate is not counted. Similarly if you want to study Engineering and then appear for JEE Mains, your 11th marks are not counted. There is no minimum agggregate requirement for JEE Mains but for JEE Advanced you will need atleast 75% in your 12th. Here again your 11th marks are not considered. If you want to study Law and appear for CLAT, again your 11th marks are not considered. But if you are planning to go abroad for further studies anytime, that is when you can apply for Improvement exams. Oversll 90% is a good score.