I think maybe you have misunderstood how the dbSizeSprite command works ?
It isnt for "resizing" the sprite, it essentially scales it. Passing a value of 100, means no scaling. So, passing 150, means it will be scaled up 1.5 times. .. So if your sprite image is loaded as a rectangle, then your sprite will be a rectangle.
You could call the dbSizeSprite command, pass a lower value than 100 for whichever side is the longer.. eg :
dbSizeSprite(2, 100, 85);
will leave the sprites x size as it is, but will reduce it's y size to 85% of what it was.
If it ain't broke.... DONT FIX IT !!!