No, you dont have to join 3 gun nation to compete, only if you want your scores to be uploaded.

In CT any club member can compete, just pay the match fee and compete.

They generally prefer if you have competed in any form of shoot, but as long as you are a safe shooter it should be ok.

When you get to the nationals you should have competed in a club match at some stage before that.

If you do want to join, there is 2 options, if you take the cheaper 45USD option you dont get the magazines.