When the school puts + or - it’s an indication of how far into this grade you are. So if you got a 7-, it’s still a 7 but just means you were closer to a 6 than an 8 for example. I think its a silly thing to add as well but i think its just so if you’re aiming for say an 8 in maths and you get an 8- you might want to put in a bit more work to secure your ability for that grade. Does that make sense?
Even thought you’re unhappy with them, these are still a strong set of predicted grades. Do you meet the entry requirements for the courses you’re applying to at sixth form? If you do then I don’t think you have anything to worry about because they’ll still give you a conditional offer for enrolment in august on the condition you get grades which meet the requirements in your actual exams.
If you dont meet the requirements for the courses you’re applying for then maybe have a word with your subject teachers and ask if they can raise your grade given that you think you’re performing better than predicted and that you’re going to work hard to increase your grade for the next set of mocks. They may be lenient, they may not be… but at least you’ll have tried. If you have guidance meetings with sixth forms you could also mention how your school calculates the grades and that you’re aiming to do better in your real exams.
Hope this helps 🙂 Also let me know if you’d like any advice on how to increase any of your grades (i got 9999998886A at GCSE so would be happy to help if i can)