CAUTION!!!
I wasn't thinking and accidentally did this, so I'm offering this as a warning to others so you don't do the same stupid mistake...
When you get to the last step in Part 2, you'll notice that you have to give 30 of the Holy Herbs to complete that step. Well, you'll also notice if you try to expand to that last area that it wants Holy Herbs as part of the items you need to expand to that spot. DON'T DO IT! Presumably that expansion location will be involved in Part 3, and we'll have time to gather those Holy Herbs in the Part 3 timeline, but don't use the one's you need in that last step of Part 2!
I did... oops...
Hope that saves someone else from making a mistake.