First of all, congrats! It's for sure a blessing and I'll pray that everything will go great this time!
I have been having weird discharges during all my pregnancy (7 weeks now) and so I had freaked out about MC before, however I just resigned and started to think in the "Today I am pregnant and I love my baby" motto.
We already saw the heartbeat with an abdominal ultrasound last week (5-6 weeks pregnancy), the doctor said it was because I am very thin, usually you don't see it from outside that early. However, she mentioned that if we wouldn't have found it with the abdominal u/s, then she would definitely have tried with trasvaginal... I really don't believe that can lead to a miscarriage...
Good luck and try to keep calm, baby can feel all your stress.