Firstly, congrats on almost finishing your degree. That's an amazing achievement. It sounds like you're pretty overwhelmed though. I'm sorry you're going through a tough time. As I student myself, I can tell you you're not alone. I finished school in 2017 and boy did I stress till I got to the end.
That breath thing you're describing? I have the exact same problem! I feel like I'm never getting enough air and I need to breathe deeper or yawn or something but I can't. And so I breathe faster and shallower and that just makes things escalate! Do you notice that it gets worse when stressed? If this is the case, it may be a symptom of your anxiety. Either way, I recommend checking in with a GP to rule out anything physiological and then if it is anxiety, you can totally see a therapist and they will help you with that! For me, exercise helps release that stress. Lying down and listening to music also helps with my breathing. Do these methods work for you?
Speaking of the anxiety, I think those negative, critical thoughts you are having like "I'm trash" often come with anxiety. So it's the anxiety talking, and you shouldn't believe that very mean voice inside your head. Have you watched this video by beyondblue about anxiety? https://www.youtube.com/watch?v=vjxhqd5QJBU It might resonate with you. If so, have you thought about getting professional help e.g. from a psychologist?
One way I use to conquer that inner critic is to think the thought "what would I say to a friend in this situation?". This might seem silly at first but sometimes I literally talk out loud to myself as if I were my own friend. You'll find that we are kinder to friends than to ourselves. So when you "role play" and treat yourself as you would a friend, you may start to see that those things you say to yourself like "I'm not good enough" are not true and that rather, you should let congratulate yourself on how far you've come and the fact that you are still fighting for academic success despite going through a tough time.
In terms of your personal statement, maybe leave it for now? You know when you get stuck on an assignment and then you leave it, go watch a movie and come back with a fresh mind? Do you think you can try the same for your personal statement?
As Donte' said, you've got plenty of time. Your journey is unique.
Hang in there, and remember the Winnie the Pooh quote "you're braver than you believe, and stronger than you seem, and smarter than you think".