If you want a wider binding - say 1/2" then you have to adjust your cut binding acordingly - probably 2 3/4" or even 3"
The width of your cut binding is in diret relation to the widgh of your seam. Do a small test piece to see what you need before cutting the entire binding and applying to quilt Fullness of the batting can make a difference as well as thickness of the fabric and even the weight of the thread. You have to account for folds.