1)what are the chances that my partner might have hsv2 at the time of encounter and not being detected in blood tests
If she was recently infected by someone else, it might now show up in the antibody test yet.
2)can I take westernblot at 12 weeks or wait for 4 months to finish after the encounter for correct results
You can take the western blot at 12 weeks, yes
3)Does any of my symptoms relate to HSV2.Also if she had hsv2 what were my chances of getting it,she did not have any lesions during my encounter
If she does have HSV 2, it would relatively new and she might be more infectious than later in infection, but we have no idea that that is the case. The symptoms that you describe on your thighs sound nothing like herpes to me.