What is the type of menu you are working with and how did you make the change to the width of the level one menu?
You should be able to account for any changes in the sizes by adjusting the margins and padding if you need to. In a quick test of a menu I just changed the width of the level one items and the level two seemed to be correctly positioned. Do you have a link where this can be seen also? Please post back with the details about the menu and any other info that you think would be helpful and we will try to help you get it working properly from within the interface.
