Taking ambulance tomorrow to appointment, very anxious.

Im 16F and have some chronic illnesses, because of this I've been bedbound for 6 months, I haven't gone out anywhere in those 6 months because of how ill I've been feeling. My anxiety has also skyrocketed and I feel a very wide variety of symptoms when I'm anxious which makes me feel like I'm dying. Tomorrow I have an appointment with a psychiatrist, ill be away from home for about 4 hours but I am so anxious, I have to take an ambulance because im not able to sit up in a car. And I just I just feel so overwhelmed and don't know how to calm down. This appointment is mandatory so I cant skip it, ill be forced to respond to questions yet I can barely talk whenever I'm anxious. I just don't know what to do to calm myself down. I've tried deep breathing, meds, distractions, ect, those barely work for me at all.

Everyone keeps telling me that I can do this but I just don't feel like I can and im getting so psyched up over this small appointment. Its lame but I just need support or advice. I'm bringing a shit load of stuff for the ride and appointment but I dunno if it'll be enough to calm me down.