Is this the test you took? https://apo-medical.cz/en/consumables/40309-mirates-syphilis-test-1-pc-4052199271859.html
I can't find a lot more about it, like what kind of test it is, but since it's looking for antibodies, it is likely an RPR or VDRL.
According to their site:
Positive result: two test strips appear in the oval hole for the test cassette. Your blood contains antibodies. P Turn bacteria that cause syphilis. It is very likely that you are infected. Contact your health care provider immediately.
Negative result: one oval strip (control) appeared in the oval test cassette. This means that the test was performed correctly and you are not infected with syphilis. However, this may also indicate that the concentration of antibodies against bacteria in the blood sample was too low to record a positive result. If any symptoms persist, we recommend that you consult a doctor.
Invalid result: there are no bands in the oval test cassette. This means that the test was not performed correctly.
It doesn't mention borders, but if you only got one strip, it means you're negative.
Is there a reason you're focused on syphilis? Syphilis is pretty uncommon around the world, and unless she had actual sores, you wouldn't get it from her.
If you're still concerned, can you go to the doctor for a syphilis test?