Do you mean you are not British, but will be moving to an English High School and would like a new 'English' name for yourself to fit it?
Carina/Karina is really lovely and easily pronounced by English people, I doubt there will be another in your school, but I wouldn't say it is traditionally English.
I would look at the latest top 100 names and pick something in the bottom half or outside of the top 100.
British people seem to be trying to be a bit more cosmopolitan with their girl names of late, taking inspiration from Scandinavia, France, Italy, Greece and even America. If you were to go too traditionally 'English' you might end up with an currently old fashioned name (Sharon, Debbie, Karen, Linda, Susan) or the dreaded 'dated' name ( such as the 80's 90's babies -Laura, Becky, Amy, Claire, Sarah, Louise).