On your LEET Classic server you must Open your app > settings > Administrators / OPs > Enter Username > Add Player. Note if your server restarts you must remove yourself from the OP list in the app then readd yourself in the app
Now about your map, I would first try and teleport away from where you spawn. Command: /tp <x> <y> <z> . The reason for there being a small little island is due to the random seed your server gets set with.
Here is a step that you can try if you can't find land, Open the LEET Classic App > Help > Repair Server > And click on the very top thing that shows on that button. That should reset your map.
* If this still didn't help please reply to this comment and I can get someone to look into your issue more.