Have you discussed options like medication or beta blockers with doctors? Beta blockers don't stop anxiety but they do help the physical symptoms. If that isn't something you'd be interested in or has been advised against by doctors you could try breathing exercises or meditations. Mindfullness is a common technique but breathing in slowly through your nose and out your mouth is something I was taught. You could discuss things like that with your therapist.
Unfortionately I don't think you can really stop it coming on unless you know what triggers it and I know there isn't always a noticable trigger. Only real way to stop each event happening is to continue improving as you have been.
I'd just like to point out that although I have suffered mh problems that involve anxiety I haven't really had much experience with proper anxiety so if I sound like i'm making no sense at parts feel free to ignore me (or correct me).
I have found that when I get stressed out some things can help me distance myself from the outside without having to leave it so maybe you can find something like that. For me music and phone games that involve my concentration and hands help distract me. TapTap revenge is something I'll use if i'm feeling stressed. I also take noise canceling headphones around with me a lot so I can use them.
Maybe you could go to a secluded spot (even the toilets) and see if you can take some time to cool down.
Whatever the case- if it works or not- please try not to be embaressed or ashamed. You are not alone and although many people will find it hard to understand what you are going through it doesn't mean it isn't tough for you. When you get anxious or embaredded remember how far you have come and that you can go even further. It's a long journey but you are capable of it as you've already shown.