I wanted to write a reply to one of the threads I'm interested in, but I accidentally clicked the wrong button. I have no idea how to delete that thread I created by mistake. What should I do?

Any admin or moderator can delete threads, just edit your post to ask for it to be deleted.
If it doesn't get picked up send us a PM

You can find the staff list here:
http://www.cosplayisland.co.uk/about