You can't get HIV when you use a condom and only the head needs protection. The condom wouldn't be loose enough that the head isn't protected or it will fall off. You shouldn't get tested for HIV - there is nothing to test for. Try to relax and move on.
You were advised previously that a duo is conclusive at 28 days not 24, but there is no reason to do another test.
No test was warranted at the first place. If the tip of your penis was covered you were never exposed. You have nothing to worry. For anxiety oriented questions, please consider the anxiety forum.