Oral contact of blood, with a mouth sore, is much less likely to infect you then, say..getting a blood transfusion, or using an infected syringe.
You should also be checked for Hepatitis A & B at the same time and get
the required shots to prevent Hepatitis A & B. Also, you wait for 12 weeks to be tested for Hepatitis C because 20% of people clear the virus on their own.
So you could test positive if you test to soon.
Best to you
It takes 3-12 weeks to appear. I would wait for 12 weeks before testing.
Best To You