I suggest that you get physical copies of the practice tests (printouts from web, or a book from store), get a room at your school or a quiet room at the library, set a timer and practice test taking there. During these practices, don’t allow yourself earbuds, snack breaks, bathroom breaks, glancing at your phone, or chattering with friends. You need to practice concentrating for 3 hours on one task in a quiet public setting. Do this twice a week until the real test. I don’t think the online tests are as helpful as the paper-and-pencil ones.