Thanks for the query.
Menstrual blood is considered as normal even if you bleed for a day.
And quantity can be as less as spotting.
There are normal physiological variations.
If you are not using any contraceptives i recommend you to get a urine pregnancy
Your symptom of spotting on the day of periods could be an implantation
bleed as well.
Once pregnancy is ruled out, there is nothing to worry.
Hope this helps.