I would guess that you would be held accountable for 1/4 of the monthly goal, but only your company can tell you that.
I would think that FMLA would cover the 3 weeks you were out, but I am guessing that your company HR would be the people to ask.
Do you have an employment contract? and does it lay these things out?
If you are held accountable. I have this info from the EEOC website
To file an FMLA complaint, individuals should contact the nearest office of the Wage and Hour Division, Employment Standards Administration, U.S. Department of Labor.
For further information, contact the Office of Legal Counsel's
Attorney of the Day at 202-663-4691.