It is happening because the logo width that you have specified is too big (500px). Please change the width to 270px in the theme options. If that doesn’t help, please paste the following code in the custom css tab of the theme optons
The logo will remain the same even if you apply the style I have given. I am not telling you to decrease the size of the logo. I find that you have given the container width too much(500px) while the logo is just 270px. The style will not decrease the logo size, but will only decrease the container width. By specifying the appropriate logo size, the logo will be centered in the mobile resolution. Thanks.