Hello there!
I can't tell you what subjects to do, in the end that is your own decision, but I will provide my own view on this. Asking people for their takes on subjects is both beneficial and confusing, because you get so many different perspectives with some people saying chem is easy, physics is easy, IPT is easy. While you should take it all into account, you are the only one who truly knows your own abilities the best. If you do find IPT that boring, unless you think it will be useful for you in the future (remember there are always various pathways to get somewhere), then it may be best to swap it for chem. But take into consideration how confident you are in chem and the time you will have to improve if you aren't as confident in it (because some Year 12 concepts require prior knowledge and if you have gaps there, you will find it very difficult, but, a lot of concepts are new as well). Check out the study designs for year 12 course, and talk to teachers in that field. All in all, if you feel like you can prepare yourself and set yourself up for a great year in chem, then do chem! But you will need to have a fairly solid understanding before next year.
I think from what you’ve said, I would encourage you to keep physics, but not to do so ‘for the sake of your atar’, because no matter how good scaling can appeal to everyone, I’ll put it bluntly, if you don’t do well, or your cohort sucks, scaling is not going to save you. BUT since you enjoy physics so much, you will put in the effort and time into it, because you want to do well and have more motivation to do so when you enjoy a subject, and it’s okay, when you do come across difficult concepts, just ensure you clear it up with your teacher straight away rather than letting it all pile up (Year 12 experience, definitely do so right away). Everyone rabbits on about the importance of chem being a prereq and to just do it, but there are always a whole bunch of ways to get to your desired career.
Do you know what you want to want to do later on (might help make the decision easier)?
Just take into account whether doing something may benefit you in the future, as well as your own strengths and weaknesses but can I stress DO NOT WORRY about how subjects will affect your atar, in the end, if you are happy with your subjects, and you do the best you can in all of them, the rest will take care of itself and fall into place.
Hope I helped you! Let me know if there is anything else you need help with at all! 😊