Is the heptane clean ? Does it evap clean, or if you put some of the pure heptane in the freezer does somethig crash out?
If your solvent is clean, no worries its just probably some more of the impurities from the plant, which you didnt see because when warm it was dissolved in the solvent, it only crashed out when cooling.. You can always recrystallize again if you want, and that should make it even cleaner.