Welcome to icliniq.com.
How are you doing?
I do not see any reason for you to worry.
Let me start by giving few basic facts about the period.
Usually, ovulation occurs on the 12th to the 16th day of periods and life of the egg is 24 hours. The life of the sperm is 72 hours. So there is no chance of the egg being available on day-5 of periods. The sperm will not survive until next ovulation. Just then, your period would have stopped, so even the inner lining of the uterus would have been so thin and unfavorable for a possible pregnancy.
So, the pill was not needed, but what you did was absolutely right as had it been a week later you had a chance of pregnancy. The pill was taken at the right time. This pill is progesterone hormone in high dose. This suddenly increases the inner lining of the uterus and makes it unfavorable for a possible pregnancy. But being a single dose of the pill, the thickness will not stand, so it will break down and you will get periods within seven to 10 days. As there was already no inner lining, the bleeding you noticed was very less. Usually, the bleeding will be thick, dark with fleshy streaks, and slightly painful.
There is absolutely no chance of pregnancy. The next period will be one month after this bleeding.
So just relax, everything is fine.
For more information consult an obstetrician and gynaecologist online --> https://www.icliniq.com/ask-a-doctor-online/obstetrician-and-gynaecologist