rigidbody to my player and a box collider to my background not working

Okay, I'm making a top-down game, where you have my player and the top down view background. I added a box collider on my player and a box collider on my background, I then added four cubes on each side on the background and took out the Mesh renderer, so it would look transparent. afterwards I added a rigidbody 2D on my player. Once done, I clicked play and my player just goes out of the background and starts acting weird, like in the inspector, the transform position and rotation for my player goes to: (on the "X" position) 0.02 and (on the "Y" position)-5.165049 (on the "Z" rotation) 0.3514884. And continues to change when I move the player. Please help!!!