Any negative is a good sign, but the accuracy is limited - that's why the 12 week guideline exists. If the test could be accurate before that time, the guidelines would be different. Unfortunately, no one can offer you odds, particularly given that you don't know the HIV status of the person you had a risk with.
PEP is highly effective, and HIV isn't that easy to transmit, so try to relax while waiting for the 12 week mark.