Never be afraid to ask questions!
I once sat in my nice warm tower after watching an a/c pushback and said
"ABC123 there appears to be a panel open on the rear port side of your a/c, just infront of and below the level of the rear door."
There was much head scratching ensued, the ground crew couldn't find it, the headset man was completely confuddled. Approximately 10 mins passed blocking the taxiway.
In the end, we got an engineer out to the aircraft, who identified the panel as " something to do with the air conditioning system".
At the time I felt silly. However, looking back on it, I am so glad i mentioned it at the time, and, if I was ever unsure again I would always ask.
The last thing I would want is to try and save my own embarrasement at the time incase I was being silly, and when the a/c commited to the air a whacking great panel fell off!
If in doubt ask - ALWAYS.