Your image is 360px X 32px. When you uploaded it to the Medial Library for your header image, did you forget to crop it properly? It should be sized 360 px X 164px.
Check the dimensions of your file image, and re-upload it. Should fix things nicely.
My image size is 360 x 117px, it appears cut off as the menu element sits over the top of it, obstructing the logo. I reduced the size from 164px as it made the header too thick.
The header image (logo) is in your css as shown above. Your min-height is commented out. That is why it showed the above dimensions. REMOVE the /* */ and it will be just fine. It’s in line 2061 of your CSS.