I click the close thread option at the bottom but I'm 99.9% sure I'm missing something because when I check back on the thread it doesn't that it's closed?
Look into the very 1st post of your thread, at the slightly upper right, beige/yellow tool bar,
you will see 'Thread Tools' 'Administrative' 'Search Thread' etc.
Click on 'Administrative' > 'Close Thread' > 'Proceed'
However, in certain forums, the Bell Tree HQ & ACNL General for example,
you cannot close your thread. Only mods/admins can do that for you, usually upon request (or complain/report). C: