how to give my students the option to "save and submit late" a quiz

[cross9]

I created the quiz with unlimited attempts, but I have this e mail from a student

"I just tried to continue Lab 47, and it also submitted it before I was finished. Usually assignments like this allowed you to do part of it and come back later, so that is what I did with these labs, however when I returned to keep working on them, it had been submitted.

It now says I have 0 attempts left, when in reality I never submitted my first attempt. I'm not sure how to solve this because if you add an attempt then I will have to start over on both 46 and 47 and I was over half way with each of them, and it took me a very long time.

Any help will be greatly appreciated. Thank you.