The page is not "too wide", there are heavy design glitches.
You have to make sure, that no element at no time is overlapping/placed outside the defined page width. This is happening on your site.
To solve your issue, please read this document: https://community.adobe.com/t5/Muse/Page-is-Shifting-Horizontally/td-p/4790837
(Unecessary for me to say, that Adobe stopped the developement of Muse and you should really think about using a different web design application. But ttelling you this, normally is Nancy’s "mission of life", Everytimes, I tried to answer a question, she will come along with this "breaking news". 🙂 )
I fixed it!
Thank you for your invaluable help!