They probably will give you a offer My predicted grade were legit TRASH. The highest i had was a 5 in math with most being a 3. My sixth form i needed 5 or 6 grade 5-9 and for math and further maths i need a 8 (which i got 4 marks off a 9) But i got a conditional offer so as long as i achieved the grades need i would get in, despite having very bad predicted grades. You should ask your school about it though. But since your an internal you will probs get an offer. I understand how you feel since i was basically worried about the same thing, Just make sure you work hard and achieve those grades.
For math i recommend doing maths genie. Doing every single one. Also for things you don't understand use gcse math tutor he explains things very well and has practise questions you can do. Also recommend maths made easy and corbettermaths also dr frost. Make sure you do these and master every topic. Also save past paper for your actually exams ,don't use them for mocks since they limited. Maths is just practise practise and more practise.
For science i just used Seneca, and Cognito(the online version) and free science lessons for notes. He very useful defo recommend him.
Sorry this is pretty long but just keep working hard and you will achieve those grades.