@tinker Try to move past this fear, for it is unfounded.
Yes, you do need to get to a certain competency level, but the level you need to be ready for playing in a group is lower than you'd expect, and, it's weirdly easier with others, because you are not saddled with responsibility for the entirety of the music. Like, as soon as you've got a single tune down, you should immediately attend an Irish music jam in your area. Immediately.
My thing is more about strings, but sticking with the whistle, one example, if you have a bodhran player in the room, you can stop worrying so much about rhythm, because the drum is providing you a pulse to follow. If you're a guitar player and someone is playing Bass, you can be way more creative with the top end and ignore your lower strings.
If I'm playing solo acoustic, I have to be alternating between bass strings on the beats, and strumming the chord in the offbeat. You cannot really do a lot of melody (that's what my mouthhole is used for, in my case), you're just a drum that does harmonies, really.
Do not be afraid. Be excited and work hard to get to that even more fun place. You're doing the worst part of this process right now, beginning any instrument suuuuuucks
@donray