This is totally normal.
What you have on a lesser car is a temperature "indicator". On most cars, it stays half way to tell you not to worry, it is within acceptable limits.
What you have on a Benz is a temperature "gauge".
It tells you degree by degree the real temp. of the coolant liquid like a real thermometer would do. Don't worry if you see the gauge going up to 90-95-100 in heavy traffic when the outside temp. is 95F. This is normal.