So disappointed and worried ?

I had my first ultrasound yesterday. I was waiting for this day to hear my baby's heartbeat. But, the hospital doesn't even have an ultrasound room. The doctor showed up with a lunch box size ultrasound machine. I was measured 8w2d exactly how it was predicted based on my lmp. I got a blurry picture (worse than my first baby's 7w ultrasound) and didn't get to hear the heartbeat. The doctor said it was too early to detect with the machine. He promised that I will hear next time and that'll be at my 18 week appt. I'm like what? I've been so anxious all this time because I had mc last time. How can the doctor be sure that the baby is growing healthy even without hearing the heartbeat? Can I trust that the baby is ok? What if the heartbeat is not high enough? Am I overreacting? Is it ok not to know the heart rate at this point? Please help!