Problem moving mail from inbox to a folder

I've made my first computer error in 2014

I have folders set up in Mail on the "On My Mac" section, one for each year. I created a 2013 folder and wanted to move all my 2013 emails (about 10,000) to this newly created folder. At first I was going to do it like I always do, hit shift and arrow down and grab about a month's worth and then right click and go "move to" 2013 until the entire inbox was moved, but then I thought what the heck, why not just do "Select all" and then move it that way. Well that was too much for the ole' Macbook Pro. After a few seconds the computer froze up and eventually when I was able to get it going again I see that:

1) Only the mails from January 1-March 13 made it to the 2013 folder; and

2) All of the mails for the entire year also remain in the inbox. i.e. instead of moving anything, it seems to have copied about a fourth of the inbox.

When I tried to repeat the process and just move one email at a time just to test it out, I get this error message: "The message “ABC” could not be moved to the mailbox “2013 — On My Mac” The operation couldn’t be completed. File exists.

But the thing is, the file does not exist in the 2013 box where I'm trying to move it.

Is there a way I can undo whatever I did and start over?