I've got too many regrets to list them all.
However I understand what you say about not becoming a decent musician. When my grandmother died (while I was still at junior school), my parents could have had the piano from her house and they offered me piano lessons. That would have meant me going to the piano teacher's house down the road though and, having been brought up never to go into the house of any adult who wasn't a family member, the thought of doing so absolutely terrified me. So I declined the offer of piano lessons.
A few years later, when I'd got more self-confidence, I asked my parents if I could have piano lessons after all but, of course, by then there was no piano available for me to practise on (and my parents certainly couldn't afford to buy one), so my request had to be turned down.
My two best friends at college were both music students (with one being an excellent clarinet player and the other being fantastic on the piano) and my total inability to play a musical instrument (beyond what I'd learnt on the descant recorder at junior school) always bugged me.