Hi, since TSECET score card is valid only for a year you will have to re-appear for it. Yes, you can re-enter and continue your studies any time you want. If you are not confident about this exam you can give other exams that you are comfortable with. There are many colleges that conduct their own entrance exams so you can check those out too. Below is a link to an article that will help you. If you still have any doubts feel free to comment. Hope this helps. All the best!

https://engineering.careers360.com/exams/ts-ecet