hi i had sex with a guy who never got tested before, we use protection while we were in the middle of it the condom slip till the head of his penis and he slide it back up, he wasn't inside me when it slip it happen just as he pull out then we continue, i took a HIV test a month after and it came out negative is that okay or do i need to get a test again? if i did get HIV can it show up after a month?