no need to be ashamed. just make sure to wear condoms.
your odds of contracting hiv from this single episode is very low.
I am not an expert like the others, but have been through the phase that your are going through.
The odds are in your favour that you did not contract HIV in the above mentioned episode.
My rationale is this
Chances of the massage parlor girl being HIV + 1in 100.
Chances of contracting in one exposure 1 in 2000
Chances that it did not show up in the 4 weeks test 1 in 10
So the odds are 1 in 2,000,000.
For your peace of mind I would suggest you get a conclusive test at 3 months expecting it to be negative.
hope this helps