I don’t know why your calves hurt, but if you are rowing correctly you will feel it in your quads, core, butt, and back. Think of it as standing up on the footstretchers and hanging your weight on the handle and pushing back. Your butt should come up off the seat a fraction as you do that. Imagine you are lifting a barbell from the floor - squat, then straighten your legs, then pull your arms and back. You are doing the same thing with the oar/erg handle, only it’s horizontal.
It’s fine if your heels come up at the top of the stroke, but the moment you start your stroke your heels should be firmly against the footstretchers, because they are carrying all the force and weight of your body.