Cannot make long posts and footer now formatted incorrectly

This is my first time editing a theme, and I’ve made an error somewhere. The theme is Floristica, and I’m working on this site for a conference.

Here’s the site: https://mams.mcgill.ca

I made the header larger so that I could put in a smoothgallery slideshow in the header. I also played with the margins for “sidebar” and “content” so that they fit with the new header size.

Now the size of the white area where I can write my pages does not change to fit the size of the content.

Also, the footer appears to be cut off (it was longer – the “CIHR” logo was in the centre), and too far right (it should be centred on the page).

I’m sure that I’ve just made a small error somewhere and I can’t find it. If you could help me, I would be so grateful.

Thank you in advance!