I'm applying for undergrad in USA. Problem is that I got terrible mid term scores in my 12th. I'm worried it will affect my application a lot. I have 1350 SAT score and descent extracurriculars.?

To apply for undergrad abroad, you need excellent profile including your class 12th marks and extracurricullars. Here you need to elaborate on your marks and the extracurricullars you have for me to check whether you are eligible to apply or not. 

Coming to your SAT score, “College range” scores are generally cited at starting at 1000, and “competitive scores” at 1200. So 1350 is good. 

Another thing that you need to consider is that the score requirements vary across schools and countries so you need to check accordingly.