Alright. Since you already did the /upgrades (attached to you), you have a choice here:
a) Leave everything as it is and wait for your leader to make the /upgrades for your shared island.
b) Convince your leader that it would make sense for you to become leader (/is makeleader playername), even if just temporarily.
(I actually had the same situation in the past^^, just talk.)
or
c) When you joined the island (/is invite playername), the island limits increased slightly (e.g. you can spawn a little more villagers at once).
If you did not join for this reason, but just to be a part of the island and have rights, you can consider making your own island for now.
For that you would leave the island (leader: /is kick playername)
and make a new one. (you: /is)
There you can build a grinder and let everyone set homes (/sethome name)
or a pwarp (/pwarp name add, then for each person: /pwarp add name playername) so all of you can share it.
And in order to still have access to the main island, tell your leader to coop you (/is coop playername).
Once activated its permanent until uncoop and you are able to do all the things you did before.
I hope this helps you decide, good luck, Calari