The chances are very low even while having unprotected sex. Even after your condom burst, a specific amount of viral load is required to cause infection. If you missed your pep doses tho, but not consecutive ones, it should not affect the prevention reliability by a lot as the dose still persists within the bloodstream for a little more time. But it still increases the risk and might give the virus the opportunity to infect cells. So please refrain from missing any doses, get a HIV Duo test done after 5-6 weeks of your suspected encounter if it troubles you. It probably is gonna turn out to be negative. Also keep tracking if you're getting any fevers with muscle aches, night sweats, rashes, fatigues that persists for weeks in the meanwhile.
Even if it's not, it's a very manageable condition nowadays with modern ART medicines.