The important thing to remember is to not get alarmed or worried if you can't find it this early. Many people can't find it until 10, 12, or even in my case, 16 weeks. If your counter is correct, right now your baby is approx the size of a sesame seed, so you can imagine how eensy-weensy tiny the heart is at this stage.
Also, when you're checking, make sure to look for the baby way down by your pubic bone, they're still nestled deep in there for a very long time. At 16 weeks, my baby is just starting to move up and out of there, but they're still pretty deep in there. It may be harder to hear just based on the location and if your bones are in the way.
So don't worry at all if you can't find it for several more weeks yet.