Hi
In the Settings dialog, make sure the check box shown below in the Layout Options tab is unchecked. It is unchecked by default. This prevents the description area overlapping the extent of your web map (either the default as-saved extent or a custom location that you apply to the map in the Story Map Series Builder). So for example you could zoom your map out a little more so more of the extent you want people to see unobscured is displayed.
If that doesn't work for you another alternative would be to use Story Map Journal, and its side panel option, instead of Story Map Series. With that option, your map (and other content) are never overlapped by the text narrative to the side of it.
Rupert