Greetings.
First of all, relax, you most probably don't have syphilis.
Primary syphilis (a single sore) only lasts one to two months and then heals on its own, then after a while secondary syphilis begins with rash all over the body.
You had protected sex, and your penis head was condom-covered, so no risk for syphilis there.
It is much less likely to get syphilis from a female CSW than from a MSM partner in the US.
And syphilis is much less common than fear of syphilis.
Anyway, any long-lasting scar on penis (especially when its cause is not trauma or is unclear) should be shown to a doctor. There are other non-STI diseases out there and some of them should be treated asap.