Thanks for your query.Based on the facts that you have posted it appears that you have protected sex with strange woman .Though you are sure of having protected sex you are worried about acquiring STD
due to using a common towel.
It is unlikely to get STD transmitted by using common towels.
However it is very difficult to make definite comment about it.
You can get your Blood Tests for STD and HIV
done to rule out the same and to be free from anxiety