Welcome to HCM
We understand your concerns
I went through your description carefully. You donot have to worry about your pregnancy
. You already had a period after the suspected intercourse. that is confirmation.
Knowing climacteric circle of a female should clear your doubts. For a chance of pregnancy, there should be a female egg to get fertilized. In your case, the egg was already in the process of disintegration and next egg comes only after 25 days or so.
Don't worry about your pregnancy.
I hope I cleared your doubt. Available for further queries.