My period app predicted me to stop ovulating on the 17th. i had unprotected sex on the 19th and he came in me. i took a plan b the same day. is there a chance i could still get pregnant?

Always, yes: Any time a fertile female has unprotected sex close to day of ovulation, a pregnancy is possible. The egg that comes out at ovulation is available to the sperm for up to 72 hours. Plan B usually works by preventing/delaying ovulation, so if you had already ovulated on the 19th, the day of intercourse, a conception & pregnancy could still be possible, so if your next period is late do preg test