After Marie rows across the river and starts walking, the boat started to float away. The first shot shows the front of the boat (pointed end) toward Marie, moving backward. The second shot shows the boat moving forward with the rear facing Marie. Then the last shot of the boat shows the front pointing toward Marie again moving backward.
After the boat starts to float away, Marie has the gun with her, but the bag was left in the boat. As she's running through the woods, she's shown in various shots and angles, the gun is no longer with her.