Help the relieved student finish their diary entry.

When the professor emailed on Friday afternoon to cancel the final essay, I was absolutely thrilled. I ______ the whole weekend trapped in the library, so I packed my bags and went to the beach instead!

The correct answer is didn't need to spend.

We use didn't need to + infinitive to express that an action was unnecessary, and the speaker knew this in advance, so they didn't do it. The student knew the essay was canceled, so they skipped the library and went to the beach.

If you use needn't have spent, it would mean the student did spend the weekend in the library, which contradicts going to the beach!