One side of my tummy tuck is more swollen. Is it because they left more fat?

This early from surgery it may only be a slight difference in swelling.  Other causes are best evaluated in-person.  Depending on the thickness of your abdominal wall prior to surgery, it is possible that one side is in fact bigger and due only to the anatomy.  Your surgeon can give a better assessment by examining you.  

Thank you for your question and I am sorry that your results have not been what you anticipated. It is difficult without an in-person examination to determine what may be taking place. Most commonly this is residual swelling from surgery which will spontaneously resolve but it would be important to voice your concerns to your surgeon to ensure that other issues are not taking place - discrete fluid collection, muscle laxity, or residual adipose tissue.

There are several possible explanations for the asymmetry.  First, your swelling may be uneven due to post operative activity or even positioning (that is, the tendency to lean towards or lay on one side more than the other).  Second, you may have developed a post operative seroma or fluid collection, accounting for the larger side.  Third, it is possible that fat removal was uneven.  I would suggest that you follow up with your operative surgeon for a careful examination and to discuss your concerns.  Best wishes for an easy recovery.