Added Smoothgallery to header – now posts too far down page

WordPress and HTML newbie, so I’m a little confused.

My site is https://mams.mcgill.ca

I used the Smoothgallery plugin from Christian Schenk to help me put a slideshow in my header. Unfortunately, when I put in the code for the images, I bump down my sidebar and my posts the same size as the photos (300 pixels).

I can fiddle with the sidebar margins to put it where I want, but I don’t have that luxury with the space for my content.

If someone could please help me with this likely easily-fixed problem, I would be much obliged!