"I didn't prepare!"

Translation: 我没有准备！

[PrestonSem]

Why don't you need a 了？

[ricky._.turner]

Would 我不准备了 work?

[golvok]

An interesting thing to say... seems to be literally "I don't have ready(ness)". I wonder if this is 'one of those things that people say to mean this' (ie. an idiom). Also, is this a valid (if maybe weird) way of saying "I don't have a plan" or "I don't have preparations"?