Hello and thank you for your question.
You may have a hemangioma
on the roof of your mouth. Or it may be normal vasculature. The best bet is to address this with your dentist
to have it viewed. The roof of your mouth is heavily vascular, you have several arteries that supply the blood from the roof of your mouth coming from foramens in your skull from behind your front teeth and next to your molars. The area if injured tends to bleed a lot and does require good pressure to gain control of the bleeding. By scratching I am assuming with a oropharyngeal tube in surgery or by accident with a tortilla chip. These items can cause trauma and cutting of the blood vessels. If you have something where you gently scratch the roof or your mouth with a finger and it bleeds then I recommend getting into a dental office for proper evaluation for pathologies.
Wishing you well and good health. I hope this helped you.