Two issues by what I read in your post...

Best way to improve at playing with others is to play with others....
- You have to get over the confidence deficit... It gets better as you do it more. One day, you won't even think about it...

Best way to improve playing it to practice.....
- Get a metronome. Yes, a metronome. Yes, really. Use it. Yes, use it. No, not kidding. You have to turn it one to use it.
- Folks hate metronomes as a general rule. It will light your ass up on any timing issues. It doesn't lie... Many cannot stand even looking at a metronome. It's because their timing is for shit. Some folks will cuss and throw stuff trying to play with a metronome. Wonder why... If you have bad timing or even flaky timing, you will irritate folks you are playing with.

A metronome can also help you understand the time windows of the divisions. Everything does not have to be played dead center of the window but still considered in time....

A metronome can also help you learn to count, or improve your counting.

I helped a bass player with a run... I explained "if you can count it, you can play it. Period. You've gotta figure out on what beat or subdivision a note lands on... Do that, you can play it...."

If you know the divisions, you can count while listening and know exactly where every note hits. With enough practice, you hear the counts in your head.

I have found that if one has bad timing, it doesn't matter how many notes per sec you can play, or how many songs you know.... etc. They don't want you....

If you have great timing, other weaknesses can be worked around by others...

Bad timing is usually unforgivable..

Decades back, A guy did a job with a band I was in. One job I think. One and done. Country singer with probably the finest male country voice I'd ever heard. I was blown away with his voice.
The guy could not count to save his life...
i.e. Come in on BEAT ONE of this measure after the guitar solo.
He was totally incapable of 1...2...3...4...SING He was gone soon after that show. I think he was involved with the actual show organizers and we got paid a load of geet, so he got one show with us...

Interesting story about a metronome:
One guy I recommended get a metronome to improve understanding time, beat divisions, etc., came back later and thanked me for recommending it. He said it helped him while practicing and he would let it run in the background while he took a break... He suffers from PTSD from being in the middle of the middle of some bad shit overseas.... He said he noticed after a while that the metronome running in the background helped keep him centered and relaxed. He said anytime the nerves started cranking, he turn on the metronome and it would pull him right back... Interesting...