Opened game boxes cannot be returned for a refund only exchanged for another disc if the disc is damaged. That is standard store policy... at least in the US. If you have already opened it then you are basically stuck with the game. You have two choice:
#1 - Buy an external DVD drive. Here's an example for $26. Power is provided through the USB cable. You will need to it install and play the Sims 3. If you go on vacation and you want to bring the laptop with you to play the Sims 3, then you need to bring the DVD drive as well...