"You better be back on the train by the end of this trip."

Aka no getting lost, Allen! Please. Does she need to set up a buddy system for you? Has it already come to that point?

But for as much as she may seem like she's just scolding him, Alice looks away then and adds: ".. But I suppose I would not mind you joining me at some point, if you'd like."

Yes, that's her tsundere way of saying she doesn't mind his company. Which is quite something, considering how picky Alice is about her company in the first place.