Gordon you might be surprised how many Minisail there are.
There used to be a great identification guide on the Minisail website, i'll need to put it back there but for the time being you can see it here: Minisail identification guide
Let us know what model you have please.
Hull and/or sailnumber; With a bit of luck you can find it stamped in the mastpot collar, if there is one. Else we can only estimate the building period.
If you are serious about getting it fit to race you might consider already contacting Morgan sails for a new sail (https://morgan-sails.com/dinghy-classes/minisail/).
Saved the easy part for last: membership. To become a member you need to own and sail a Minisail, that's all.