Actually Zoe
I assume that the mega menu component that you are having issue with at lower breakpoint is the component available from CoffeeCup's Component Thingy (The Free One) And it's the "Foundation" one, not Inger's one from her mock up page.

If it's the one from CoffeeCup's Components, Then there are 2 issues.

AT The LOWEST BREAKPOINT (480px) you need to move the slider indicator just to the left, of that.

Step 1/ Select the container "navbar.dd
Change the "Layout" "Flex" from nowrap] to wrap
Optional to change justify to "Space Around" or Space Between" up to you

Step 2/ Select The container "dropdown-content"
Go to the "Layout" tab "Position"
Change the top selector from 60px to "Auto"

BOOM there you have it.

This is obviously editing the "Component AS IT IS from CoffeeCup.components downloaded because seeing as we cannot see if you have added anything or taken anything away etc. but the principle should be the same if you have added/taken away anything


Ingers version available from her mock up page works perfectly without need to edit