You can change the style with CSS if you want to. What’s the URL of your website?
URL is: http://www.four-ward.com/stores/
Also when you check on mobile phone, the location field doesn’t scale nicely. Can i change that too?
The reason it looks like this is because of your template. The div holding the store locator is set 67% wide, instead of 100%.
You can try to and change the CSS rules ( you can check the applied CSS rule in the developer tools in your favorite browser ). Or you can simply create a new template yourself.
You theme also seem to be using AJAX to load the content of the different pages in the background? This will also cause problem for the map, so you should disable that.
Another problem is that the Google Maps library is loaded twice, and this will also cause problems. You can see this by viewing the source code of your page ( ctrl + u in Firefox ) and search for maps.google.com. You will two hits.
The first one comes from the contact form maker, which breaks it. Disabling that plugin, and using anther contact form plugin that doesn’t load Google Maps will fix this. This is not a problem caused by the WPSL plugin, but simply a problem with different plugins trying to load the Google Maps library when it’s not necessary, and thereby breaking other scripts.