Submenu on mobile alignment

Hi!

I really love this plugin, it does exactly what I need, I just have one minor issue I cant seem to figure out.
I hope you can help, since the site is not live yet, so I can’t show you a working version of my problem.

My menu is looking great, so really happy there. I have all top level pages, and one of the toplevel pages has 4 sublevel pages. It shows an arrow next to the item in the menu, and when i click it, it unfolds nicely. The mobile version however, the dropdown of the submenu, when i click the arrow, is aligned to the right, so far it looks like it is cut of.

I cant seem to find the right settings or css to align these items directly underneath the parent item. I made a screenshot to clarify:
http://bijadenan.nl/wp-content/uploads/2017/09/Screen-Shot-2017-09-14-at-21.32.23.png

I hope you have an idea on how to fix this!
Thanks in advance!

The page I need help with: [log in to see the link]