add slide-in exception for 404 error using custom 404 plugin

Hi, I have created a left hand slide in for desktop users who are viewing pages because that's where my whitespace is, and a right hand for posts since my whitespace is on the right.
It works perfectly well except in the case of a 404 error in which both slide ins are presented. I'm using custom 404 and have my 404 page set to I added an exception for that URL and the exception works if I navigate to

However, if I navigate to a page that doesn't exist (for example "") both slide-ins appear. Is there a way to add an exception in the case of a 404 error?