Hi,

It should be auto re-size to fit with your screen. Because a lot of logo image in landscape size.

You can add more this code to Customize > Custom CSS to resize it like you want:

\
@media only screen and (max-width: 480px){\
#logo a { max-width: 150px; }\
}

Change value 150 to value you want.

Best Regards,

PenciDesign