What size are you selecting when using the GFP widget?
You can add your own sizes in your functions file. Look for something like this and then create your own –
//* Add new image sizes
add_image_size( 'featured-content-lg', 1200, 600, TRUE );
add_image_size( 'featured-content-sm', 600, 400, TRUE );
add_image_size( 'featured-content-th', 740, 340, TRUE );