Does the bag have a shaped edge or is it just not perfectly straight?
If it is not perfectly straight and you want it to be, then go on and make it straight cutting with your rotary cutter and a ruler.
If it is a shaped edge, then use bias tape and bind like you would a quilt.
Or if you do not already have the bag stitched together, you can do like I did on one I made, that I did a piped seam as part of the initial construction. PM me for more info on how I did this if you want to try this option.