I sort of got worried about this in the past too. But I have to say cars will run hot in certain conditions, which IS normal, as long as it doesn't redline. So if it's a really hot summer day, it's normal to run in the 100 even 110 if you have the air condition on. Slow traffic adds a lot to it coz you're not getting cooler air, you're getting the air from the exhausts of other cars in front of you (I noticed this at an automatic car wash once trust me). So I would only worry if it got really hot in normal conditions. My mechanic once told me too that the 95 C280s do get hot in there coz of the relatively big 6 inline.
So notice the conditions you're driving in. And it never hurts to run checks on the car.