Doppler worrier

I have the Wusic Doppler and was able to hear a heartbeat in the lower left of my uterus at around 11 weeks or late 10 weeks. I'm now 12 weeks exactly and can't find it at all. All I hear is mine and though yesterday I heard some movement I didn't hear anything today. My next appt is not until 8/11 and I'll be traveling for work until then so now I'm going to be worried the entire time. I do have a Retroverted uterus but I heard it corrects itself around now.