I agree...Journey to the Interior is about how crazy and unpredictable an imaginative journey can be
--dark imagery of "trees grow spindly; with their roots often in swamps"; description of physical environment metaphoric of psyche
It also recognises that the obstacles are fictional and made up (hence journey to the "Interior"). However, it also recognises that just because the challenges aren't real, it doesnt mean that it is easy to overcome them. This is like the Wizard of Oz, how it is just a dream (right? i think thats the ending - its been a while since I've seen it). Also, how the Wizard is just an illusion (guy behind the curtain) - reflects that just because something isnt real doesnt mean it isnt scary or powerful.
-- desperate tone of "whatever I do I must keep my head" similar to Dorothy's "theres no place like home..."
Anyway, I hope that helps a bit with ur Wizard of Oz reference, sorry if its too late for your assessment (you can always put it in your trials!!). Btw, dont worry if it seems too complex a text, Atwood can do that to your brain. It really isnt that hard to fit into an essay.
Good luck!!