To confirm, is the list of gas stations coming from data that you’ve uploaded or are they from Bubble’s geographic places search?
When you have your own data entries and format the field type as an “address”, then you have the ability to do restricted geographic searches by radius. (If they are uploaded as “text”, then you can’t create a geographically restricted search…at least not easily).
Otherwise, if you install Bubble’s “Google Places” plugin, you can do a geographically-limited search based on Google’s Places API search for a specific type of venue (ie. gas station).
For both cases, you’ll want to familiarize yourself with Bubble’s concept of current geographic position. Here’s a quick tutorial.