Minecraft WallMap with Zoomed out MAPS

From the Wiki (emphasis mine):

The map does not center on the player when created, rather, the world is broken up into large invisible grid squares, and the map displays the area of whichever grid square it is in when it is first used. [...] To make a map that is not identical to the first one, the player would have to move outside of the edges of the first map (because then they would be in a new grid square). This way, no two maps of the same size can ever partially overlap and every map can display only a fixed area.

The catch here is that your second map is a different size to the your first, so only walking a short distance (i.e. just outside the boundary) means that the center of your second map overlaps with the area of your first, once you expand it.

This table shows the area that each map size covers. In your case, a base zoom size covers a 128 x 128 block area (or 4 chunks). Zoom 1 covers a 256 x 256 area (or 16 chunks). So in order to match up the borders and allow for the expansion of your maps, you will need to accommodate for that extra boundary.

You can use the hotkey F3 + G (Or Fn + F3 + G on some keyboards) to show chunk borders to count the chunks before you use your map.

Ultimately, when playing with map sizes that are anything other than the base level, or max level zoom, it can be tricky to coordinate the borders to match up.
Locator maps can help you better achieve this, although you may still run into difficulties.