Hi My Name Is Olivia And I'm 17 Years Old.

Hi my name is Olivia and I'm 17 years old. I've been given norethisterone tablets for the first time to delay my period whilst I go to a festival. However, I have only started taking them for one day and I am sensing the start of my period, eg: cramps and slightly tinted urine. If I carry on with the norethisterone will it still continue to postpone my period even though I may have taken it too late?