Hcg levels

Guys I found I'm pregnant October 1st and it's my first pregnancy and I'm supposedly 4 weeks but they took my levels and it was 310 then dropped to 260 something hopefully a miracle happens because I hear the stories. So I'm gonna pray for a miracle. But I don't get why she wants to do an ultrasound blood test, and possibly heartbeat. 2 weeks from now. At least my levels didn't drop terribly..I didn't pass anything that looks like a miscarriage