You’d better wake up early then.

[keannu]

It's hard to understand why the answer is 1 to this question. Did he(M) mean that as her afternoon classes are full, she'd better fill her Spanish and Astronomy classes into morning time, which would make her get up early?

W: What’s up, Chris?
M: Not much, Alicia. What are you doing now?
W: I’m just looking at the class schedule for next semester.
M: Oh, you haven’t registered yet?
W: No...it’s hard to choose my elective courses.
M: What’s hard about that? You only have to choose classes you are interested in.
W: That’s the easy part. I’ve already decided to take Spanish and Astronomy.
M: So, what’s the problem?
W: The afternoon classes are all full. Only morning classes are open.
M: ①


① You’d better wake up early then.
② You’ve finished registering classes.
③ You can take them in the afternoon.
④ You can go to Spain to study Spanish.
⑤ I have no time to check the class schedule.

[Rover_KE]

Did he(M) mean that as her afternoon classes are full, she'd better fill her Spanish and Astronomy classes into morning time, which would make her get up early?

Yes. It's the only answer that makes any sense.

Rover

[keannu]

Following the reason I gave?

[bhaisahab]

Following the reason I gave?

Following the logic of the dialogue it's the only one that makes sense.