Photoshop GF problems

Hello! I have a problem I would really appreciate some help with. Every time I use photoshop AI, when I select the background and change it, the product itself also changes. For example if I use generative fill to change the background behind a bottle. Then the bottle becomes bigger (the edges change). It happens every time I use the function. Although I'm very happy with the background, I can't use it because the product looks weird. Really appreciated the help, have watched all sorts of videos.