It is best if a corset fabric doesn't stretch. You would be surprised ... most non-stretch woven fabrics have some give in them, usually on the cross grain. So, try stretching your fabric sideways and lengthwise. You might consider cutting the pieces sideways so the fibers going around your body are actually the straight grain of the fabric. Or, if you are using an extra inner layer like I am, cut it sideways.
And here is a little secret ... you can tack bust pads to the seam allowances to fill out and give a little lift to the bosom, if you want.
I'm going to write more about corsets next week, discussing fabric, boning, grommet and lacing options. There are many, each being good for different situations.
Yes ... sometimes we don't need anything better than plastic feather boning.