Do you mean that you posted, but your post stayed in the post composer so you thought that it didn't post and you posted it again? It saves a draft of your post in case anything happens, and sometimes it doesn't delete the draft after you post it. It's usually if you have more than one tab open (the other tab can remember your draft post, but won't know that you posted it)... I'm not sure, but maybe an internet connection issue could also cause it.this might be the fault of slow internet but I was editing a post where my text got stuck in the quote box and the completed edit created a new post. so i went back to edit the original post to look more normal and to apologize for the double post... now i've posted three times and look like a tard. worst thing is my original post is still lost in the quote box. I don't dare edit again, but now I am a three in a row poster who can't get out of the quote box, this is my one and only argument for having a delete feature.
I'm gonna edit this post and see if this happens again
edit: if you're reading this in one post its fixed. it was probably my shit internet
Refresh the page just to make sure (and be mindful that your post might have created a new page), and if your post was actually posted successfully, just delete the draft (there's a "Delete draft" option in the post formatting tools under the floppy disk icon).
To edit the post, you just click the edit button underneath it. Then your post will be replaced by an editor where you can edit your post and and save the edit. Unfortunately the "insert quotes" option isn't available on that editor; if you want to add any more quotes to it you have to insert them into the new post composer (which is at the very bottom of the page) and cut-and-paste that code into the editor.