Be clear regarding the already selected gallery. That can help indicate that only one is selectable, and that it's currently being used.
My opinion (no research!) is that what's more unclear is the fact that the gallery with the heart is actually being used. This arose because of what the icon could potentially communicate.
You're using the heart icon, which is often used to communicate 'I like this', not necessarily 'This is currently in use' (and is the only one being used).
The Nielsen Norman Group has some good resources re: icons and text labels for clarity:
From Yes, icons need text labels:
Universal icons are rare. To help overcome the ambiguity that almost all icons face, a text label must be present alongside an icon to clarify its meaning.
There might be better phrasing for
use this gallery (it actually seems fairly clear), but equally important is clear status indication about what's currently selected (and used).