Hi and thanks for this query.
I am so sorry to hear about these troubling events and findings. Looking at them critically, if the test that was done last month is PCR(looks for the virus), then for real you didn't contract
HIV from this encounter.
Irrespective of the results, the chances of contracting HIV from an encounter like this are very very small. The blade must have been used by an HIV+ individual within hours of you using it and sustained a cut. These events all together are very unlikely to have happened exactly this way and you using it shortly. I am pretty confident you are not infected from this encounter.
However, follow up with a test at 3months and all the doubts and guessing would be over.
Please, make sure you always use a new blade all the times and don't share it with others. In addition to avoiding using and sharing sharp objects, always use a protective method during intercourse.
Hope this helps and answers your query.
Feel free to ask follow up questions.
Wish you well and relieve yourself of the worries while taking active measure to prevent future exposures.
Dr, Ditah, MD