Hi Danielle. If you put the lens straight back onto the camera with the reverse adapter then you will never get anything in focus. They are designed to have a st of extension tubes or a set of bellows between the lens and the camera. After that, your subject should be about as far in "front" of the back of the lens as the sensor is behind it normally. AND, no matter what, your subjects will always have to be pretty close to the back of the reversed lens. It is a system that can give pretty large magnifications but with fairly exacting conditions for focus.

As to the Q of it being "locked". I can only suspect that you need to put your camera into manual mode for a start. If the problem persists, then I would be wondering about the compatibility of that reverse adapter for your camera.
Am.