Hi I Was Given Metrogyl 2oomg For Very Bad Gum

Hi i was given Metrogyl 2oomg for very bad gum infection i was told to take 1 3 times a day for 3 days ....Thing is there are 21 tablets in the bottle i'm on my 3rd day but dosen't seem to be helping do i finish the course or stop at the nine tablets Thank you