Menu on iPhone (landscape) not selectable

I have added a few items to the main menu and generally everything is working fine. When I view my test page on the iPhone (in landscape mode) and expand the menu, there are too many items to be viewed on the screen and it is not possible to select the last one or two items on the menu.

https://www.miannegolf.com/mbtestsite

I have a Child-theme where I have made some modifications to some of the formatting. Is it possible to make the menu scrollable, for example? I guess I can look this up on help files for CSS, but would be nice if someone has come across this issue before and has a fix?

Thanks ??