And even if the last scene with Marco not remembering his password of his laptop seems unsettling I think it was there to remind us that what happened to Marco in that dimension DID happened, but he is in the process to going back to his 14 yearls old self. His mental state is not going to return to his normal age as fast as his body, because if that happened, it would have been disturbing for him.
The next scene is what, at least for me, proves my point
That means he did remembers the burger, that he bought that and that’s why he says “Still warm”. This is showing us that he is starting to going back to his old mental self.
“Alright, let’s go for a walk”
He still remembers this and it’s not doubtfoul of what the puppies want and he is doing it with a smile. He is sure of what he needs to do, something that didnt happened with the laptop. I think by this moment confirms that he is back to being 14-years-old Marco.
So this scene is actually shwoing us a slower process of him regaining his 14-old mind. Mind and body are different things and I think this is very realistic in the point of handling differently a body change with a mental change. You cant just show two different realities to someone an expect them to addapt quickly to them. It took a little more time that his body, but he is back to his teenage mental state.
His memories of what happened in those 16 years will go away? Probably not. But he isn’t going to remember it as “what-i-am-now” but a “what-i-can probably-be” more likely scenario. That he can have a future if he proposes things.
With the experience he gained, he is going to enjoy his teenage life with his friends and family.