YOU didn't posses a risk from this incident.
Firstly, your assumption of your partner being HIV positive is anxiety driven and is baseless.
As suggested to you already, the urethra was covered and therefore, there was no scope of transmission for infected fluid. Infected fluid can't mysteriously crawl up from the sides of the penis in to the urethra, this is not logical.
There is no point of doing "what-if" any further, the information provided to you is clear-cut; "if the tip is protected, you are safe". If you are unable to rationalize, see a therapist.
As long as the head of his penis was covered, he was protected. So, if it pulled up a bit at the base, this would not affect efficacy of the condom and he had safe sex. Testing, for general information, can take place at 28 days and beyond with a 4th generation Duo test but it doesn't sound like he needs to test.