tooth tipping

[diehard]

before i started my treatment i had a letter telling me i needed 4 teeth extracting and there is a 15% chance that at the end of treatment i may need to wear a fixed brace as some back teeth may tip slightly and need uprighting, i fear this may be happening with 1 tooth in particular when i put tray on it goes on but does not look quite right. Im not sure about the cost of needing a fixed brace after invisalign because i dont want to pay thousands more for a few months instead of a few years. The letter also said there was a 20% chance of a mid-course correction new impressions ect.