I used to sail Enterprise dingies years ago and sometimes used to get trapped under the sail during a capsize. First time was scary as I also had a foot trapped in my foot straps.
I wasn't calm, I was panicing and under such a situation I went route one, pushing the sail up to give me breathing space. Adreneline in such situations gives you extra physical strength, but once Id had that first breath, then i calmed and simply stopped squirming and slid my foot out easily.
I just remember the cold, it was a reservoir in the North of England in April lol....
You did a million times better than me, you stayed calm, the situation was sortable and you sorted it. Well done to you. Be proud of yourself, you already know never to underestimate the water :-)