Definitely discuss with your teachers, they will be using the evidence they have to decide on most likely grades - they don't pluck the predicteds out of the air
Its important to be honest with each other, they will have seen other students in previous years and know how they got on - you will probably have a sense of where you are working grade wise - its a bit of guess work getting these predictions "right"
An example, not a million miles from where you are - my youngest is in Yr13 and got CCC in her latest mocks, she is certainly able to get to BBB and the school was okay putting ABB in UCAS. The unis she wants are all AAB to BBB.
If things go well in her A Levels she will hopefully get her Firm with ABB (unless its elite uni or a competitive course, most unis usually accept a dropped grade). If she gets BBB her Insurance will hopefully take her, if not then she will be in Clearing - she has already applied to her Clearing choice knowing she wont Firm or Insure with them - definitely don't wait until Clearing, apply for some between now and January. Clearing is your safety net if the results are lower then you hope