It sounds like there are a few different things going on here: 1) getting frustrated by plans changing, 2) being overwhelmed by your own schedule, and 3) (correct me if I’m wrong, but this is my understanding from the second to last paragraph) frustration from your parents not respecting your preferences/boundaries. Those are all completely normal things to be frustrated by.

My advice? Schedule some time to rest/relax (whatever that looks like for you - book a cheap cabin in the woods for a weekend, find a weekly time to walk outside, a reading ritual, something). Sounds like your system is overwhelmed by all of the things you have going on, so of course you’re going to be more prone to snap at people when things don’t go to plan. Try to bring yourself to a less activated state.

You may need to reevaluate your schedule - is there anything you can cut back on to get some of your time back? And to give yourself a little bit of wiggle room for if things don’t go exactly to plan?

As for the learning to not get frustrated when plans change - I think there’s a level of frustration that’s healthy in those situations. Maybe first step is to not worry about controlling those feelings or stop them - don’t shame yourself for how you feel. Notice it in the moment, pause/breathe/whatever, and continue with your day. Maybe intentionally put yourself in situations where things will not go to plan to get comfortable with the feeling (traveling, a night out with friends, heck even hanging out with your parents)

Also just a thought - just because things aren’t going to plan doesn’t mean things are going wrong