Website not resizing certain elements at different screen sizes.

For some reason my client's website does not seem to be resizing elements correctly at smaller screen size. Some sections change to the correct screen size while others do not change and overhang to the right side leaving a large white gap. I have had to fake some of the sections with shapes as coloured backgrounds so that some elements can overlap. Could this be what is causing the issue? 

Website is www.innerdimensionpsychology.squarespace.com and can be accessed with the password 'IDP2024'.