Ofc you can.
1. Prelims don't count for anything
2. You have 2 stress-free weeks ahead of you
3. Countless people before you have not excelled in prelims but have gotten great HSC marks
Main things to make sure that you understand (or at least what I think):
- Mole calculations
- Chemical equations (balancing and common ones, eg. Acid + Metal -> Metal Salt + Hydrogen Gas)
- Bonding
- Basic trends of the Periodic Table
- Solubility
- q = mCdeltaT
1. Apparently it is easier because it is more about applications rather than new concepts
2. Yes
3. Probably don't need to catch up
If you think that you'll enjoy chem more, do chem