Your question has been fully answered. We are sorry you are so anxious and we suggest you talk to your doctor about anxiety for help.
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You had no risk for any STD from this encounter.
Syphilis is transmitted by direct skin to skin contact with a sore, almost always mouth to genital, genital to genital, or genital to anal.
Hepatitis C is transmitted only by blood, and is rarely transmitted sexually. When it is, it's usually by anal sex.
If she had no contact with your penis at all, and you had no contact with her vaginal area, you can't have an STD.
I don't know about the pimple on your stomach, but it's not an STD. If it lingers for more than a day or two, or it gets really red, hot to the touch, or you get a fever, go to the doctor.