I think a lot of people can get discouraged by poor mock grades, but my honest opinion is that if you can see that something hasn't worked for you in the run up to these mocks, try something new and work hard. The advice given by my teachers to those students who want to up their predicted grades and gain better marks in future mocks and the real exams is to work hard, ask for extra tasks/attend revision sessions, or try and get a 1:1 with your teacher just to get that specific advice for you. If you're getting A*s in your class tests then assuredly it is possible and achievable in your exams, I think getting a fresh start in the next set of mocks, and following through with your progress in class exams will help keep that same feeling for your mocks so you can get the grades you want.