Hey Bang Boom Ben, unless you use the [Scale to fit composition] feature when you right click on a clip, your cam should come up at its native resolution (800x600?). Note that when you use capture cards instead of a cam, you have to set the resolution to match the source.
Once your clip is loaded you can change its size by using the resize button which cycle through various sizes (comp height & width, comp height, comp width & clip native size) :