If you go with that route, for your "actual days worked" you'd have to put the number of days you were "available" to work for your employer, i.e. the number of days they've said you worked for them.
Technically, the information you received is wrong, you do have to complete three months of work. BUT... almost no one does, because most farmers are happy to sign them off for the full 3 months, regardless of whether it was completed. As long as your records, and the farms records of your work matches, that is enough to pass any auditing that immigration decides to do. And even then, they rarely (I've heard 5-10%) check anything beyond what you filled out on your application.
If you're still not happy with that, then just do the full 3 months. Then you've definitely qualified.