I lost my first baby at 7 weeks because a heartbeat could not be detected. My doctor did a traditional vaginal ultrasound first, then used a more sophisticated machine right after (have no clue what it is called). The second ultrasound had the capability of showing blood flow to and from the placenta (showed up as red and blue), any sort of action within the uterus, and also had thermal imaging. In addition to not seeing the 'flicker' of a heartbeat on the tradition ultrasound, the second ultrasound clearly showed that nothing was going on.
In my opinion, wait it out for the second ultrasound just to be sure. There's no harm in doing so, and at least you may have peace of mind that you waited to be certain.
As for miscarriage, I think it depends on a number of factors. How old are you? Have you had any other reproductive health issues? How eager are you to have a baby? Your doctor is fairly aware of your reproductive health - what is his/her opinion? Because I had major infertility problems, my doctor wanted me to give it time to try to let my body resolve the miscarriage. I finally miscarried about 2 months after we knew the pregnancy failed. Quite honestly, the physical act of the miscarriage wasn't that bad - feel free to PM me with questions about what to expect if you'd like.
And...we received miraculous news 2 months later that we were pregnant - spontaneously and without drugs (given my reproductive issues, this clearly was an anomaly)!
Give yourself time to grieve your baby. Surround yourself with family and your support system. And when you are ready again, if you want to try again, just be positive because (as you can see in the responses to your post) there are many, many, many success stories.