With the eCVT, the sound of the engine does not correlate with your speed, but with the power that you are requesting from the car.
It will get loud (high RPMs) when you are asking it to go up a long/steep mountain, or heavy acceleration. But, going downhill, the engine may not even be burning fuel (essentially off).
The gasoline engine is RPM limited at 4500 (Classic) for 5000 (2004-current), so it never gets to a red-line situation.
Don't worry, and just drive it! (unless you actually get a high temperature warning light, but I've never heard of that happening unless the car was already having mechanical difficulties and was in
110+F degree weather for several days...)