Hi, "is_something_wrong" is exactly right. I am a technician that does echocardiograms. How long the test takes depends on how easy it is to get the pictures, and also if there's anything wrong with your heart. If you are young, thin, and have a healthy heart, 10 min is about right. If a patient comes in with lung disease, is extremely obese, or has significant valvular disease, it could take up to 45 minutes. So with you being 18, I assume you don't have lung disease, and you're probably in good health, I would bet your images were easy to obtain and so it was a quick test. Hope this helps.
I think I was told mine would take 30 mind when it only took 10mins. They probably just tell you a certain amount of time incase they need extra time to look at it all. I wouldn't worry.
An ultrasound of the heart doesn't take more than 5-10 minutes. The fact that the examination was quick is a good sign, nothing probably needed more evaluation, and your heart was easily visible.
Of course, none of us can say what the results were, but do not worry about the time. It's normal. When I had an echo done, it only took a few minutes and everything was normal.