Invisible left sidebar

I am very new to this website-building thing and loathe to mess around with coding. I changed my theme and things were going nicely, until I realised I must have a hidden side-bar on my Home page because no matter what I try I can’t get my columns to start over at the left.

If anyone can help me find where this thing might be lurking so I can remove it, that would be much appreciated 🙂