Can i please ask that you wait and get a second opinion. You are SO early that it could be just too early to see anything properly.

If it is a miscarriage i am so sorry, as having just gone through one myself it is awful and please take care.
Yes, that - there could be many reasons that there is no heart beat yet - doesn't mean that the baby isn't viable at all! PLease don't take the word of one medical person as the truth. Leave it a couple more weeks to be sure - there is not going to be any harm done by waiting - if it's a miscarriage then your body may well lose the baby naturally anyway.
I have a friend who was told that there was no heartbeat in her bub like you, he is now a nearly 2 year old healthy boy!