was expecting my period on 23rd March, but I had spotting till the 25th

First of all, you should have mentioned how many days your period usually lasts. If it lasts around 4 days, then the bleeding you had was just normal but was 2 days delayed. In this case, the first day of your period is 25th march. In case your period lasts longer than 4 days, say around 6 days, then the spotting you had might have been the part of your period but it was just not in the amounts you used to have as you might have caught some slight cold so your period became a bit irregular because of it.
How many days this spotting lasted, by the ways?
However, according to these facts you mentioned, the first day of your period was 23rd march and you can use this date for counting your cycle.