Reminds me a bit of the first jam I ever joined. It was a 72 hour Ludum Dare and I delayed a feature which I thought would be easy to implement, but pretty essential to the gameplay for the last day (my priorities back then were quite skewed, as I remember having a working splash screen and a menu before the actual game worked x)). Of course it wasn't easy to implement and we ended up having to redesign a large part of the game to make it at least somewhat playable in the last few hours of the jam. Boy was I feeling frustrated...
I guess what I'm trying to say is that you should take it as a learning experience and not be too hard on yourself. Game jams are full of suprises!