You don’t have to do it every 2hrs. Choose a time range when baby is most active (either morning or night), and began counting. If you feel baby is kicking lesser than usual, you need to call the hospital for a check.
There's a 'Kick Counter' on this app itself. Use it to count your baby's kicks. Every movement is counted as a kick. Necessary especially for the last stage of pregnancy to prevent from stillbirth.