don't need to/needn't

Hey.
I think know everything about this thing exept for one.
Exaple:
We neednt have taken an umbrela cuz it didnt rain(that means it wasnt necessary, but we did it anyway)

We didnt need to take an umberla cuz it didnt rain (that means it wasnt necessary so we didn't do it)

Thas what they told us at school. But I just have this feeling there s gotta be a way how to express the first one without using 'neednt have'.