invalid product key

I have downloaded a trail offer of office home and student. When it gave me
the product key i wrote it down wrong. It was suppose to be e-mailed to me
but it never was. So I requested another one. This one is saying invalid
key. What should I do? I have called the microsoft people and they send me
to this website. Please help, I can only use it a limited number of times
before I have to put it in, eventhough it is a 60 free trail.
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wife, mother of 4 and student