Feeling Absolutely Embarrassed

So this week I've spent the last 4 days dog sitting for my Aunt. And I traded places with my mom basically where she took me home and my mom would watch the dogs for the night. My boyfriend of 3 years came home from work a couple hours later after I came home. He pretty much dragged me out to this event with his friends which I allowed because it made him happy and he was very excited. It was a graduation parade for his coworkers and friend's school. So we went to get food before the parade started. The Ice Cream shop was too packed for my liking. The other dessert shop wasn't much better. But was... acceptable. So we eat on some sweets and leave to find my boyfriend's friend's and coworkers. Immediately I felt completely overwhelmed and moved away from everyone and chose to sit alone nearby. My boyfriend finally caught on that I wasn't feeling right. He asked me several times if I wanted to leave to which I responded by explaining that I was going into the stages of a panic attack. And was trying really hard to resist stemming in front of everyone. When I stem, I pick at my lip skin, break off my nails, mess with my hair, hug myself, fidget with anything I can get my hands on and even scratch myself on my arms until I'm in extreme pain. It's embarrassing to do such things in front of my own family members who have seen this over my 26+ years. It's another kind of embarrassing to do it in a coward of hundreds of people including my partners friend's and such. Eventually we were going to move through the crowd to another place with his other friends. I didn't feel comfortable at all and my boyfriend could tell. He said he understood if I wanted to leave and meet him after the parade. To which I reluctantly said I would go somewhere else, as I didn't actually WANT to leave his side, but I definitely did NOT want to be there in that crowd. So I walked the opposite direction as weakly as I could and when I was at a safe distance away, I let myself stem the whole way to a shopping center, scratching myself into extreme pain because I don't have my fidgets. Eventually I walked to a few stores to clear my head and recuperate with some AC. When the parade was finished I walked back and met my boyfriend a block away from where I left him. Now we're sitting on a bench trying to think of what food to eat and I'm trying this hoping that knowing if someone else has gone through a similar situation, they could let me know so I don't feel so embarrassed about it when I talk to him in a little bit.

Please, if I'm not alone, I need to know. I feel absolutely embarrassed and terrible that I just left my partner when he was excited that we were going to do something together with his friends.