Syphilis is transmitted by a direct skin-to-skin contact with an open lesion of an infected person.
It is theoretically possible to get syphilis from the exposure you described. But it is highly unlikely.
Your risk is only theoretical, as there are too many "if"s involved. If she was infected (highly unlikely for a masseuse, since they are usually very careful about skin conditions and possible lesions), if she was in the infective stage of disease, if she had a lesion at the place of contact (which you didn't see), if there was enough contact for the bacteria to infiltrate... your chances are slim to none.
Postexposure prophylaxis is available but is normally prescribed when the risk is high (like after unprotected penetrative sex). You may discuss it with your doctor, though I think it would be an overreaction. Self-medication is always a bad idea.
The good time to test for syphilis is 5-6 weeks. 2-3 weeks is too early.
I wouldn't worry about the sex with your girlfriend since your exposure was very low risk. But if you want to be super-safe, you may stick to protected sex for now.