used 2007 335i

I just bought a used 2007 335i that has 40K miles. Although I got the extended warranty and had my mechanic check it, I am worried that I will start having problems within the next 2 years. Can someone tell me if they've had problems with their used car? Someone told me that because it wasn't driven as much, I will start having engine and transmission problems. I need advise as I have a few more days before I can return it to the dealer. Thank you.

used 2007 335i