Other mistake: They make it clear to us that the portals are one-way gates (from origination to destination). However, the last portal is two-way.
Continuity mistake: Roland crumbles up Jake's drawing and stuffs it in his jacket, but when he takes it out again, it's neatly folded.
Suggested correction: He doesn't crumple it up, he folds it. Though he does stuff it roughly into his jacket.
Phixius ★