Did you finish your game? Did you almost finish your game? Did you have Quite A Few Problems And Maybe Did Not Finish That Game? That's fine!
Write a post-mortem!
A post-mortem is an analysis of a project's process--what was successful and what was less successful? The purpose of a post-mortem is to understand what really worked for you or your team and what broke down. Did you struggle or get stuck on one mechanic? Did your team communicate well? Did your audio person have enough resources to work with?
You can write your post-mortem as a final post to your devlog (and we encourage it for consistency!) or you can post it as a separate thread with [Post-mortem] as a tag in the title.
Check out these post-mortems on Gamasutra for some inspiration (and maybe see if you can find your favorite titles!) Don't feel that you have to match the tone of these articles, though. Your post-mortem for the jam can be as formal or as informal as you'd like--all you really need to document is what worked and what didn't!