School scavenger hunt is a good idea.

Make a list of things to find, and they need to take a picture of it.

I've done it before, and the student enjoyed it.

I also made some what happens next games. It can take up 20 minutes.

http://www.waygook.org/index.php?topic=48652.0

What I normally do to make the afterschool class fun is to make teams. Have a competition with points, and then the winning team gets a prize like a 1,500 box of cookies.

Question - why did they sign up for an English after-school class if they had no interest in learning/playing English games?

Sounds to me, like you got a bunch of 'we don't care about school' type of kiddos who chose your class thinking that they'd be able to do whatever they wanted (if they were to sign up for another class, there wouldn't have that sort of freedom).

Anyways, student-centered class ideas are a good start.  Do crosswords, word searches, grammar worksheets - tell them that they have to complete these before the class is over, or they'll have to stay after-class.

Also tell them that they have to work seperately, not in teams. 

Or - pair up the best student with the worst student in your class - have them teach a certain grammar/writing/speaking point - at the end of the day, do a competition, the best pair wins.  Or have no competition, just do a mini-test, if the low-level student does well, award both students. 

Or - assign the best students as teachers - have them teach any English aspect they want (though you could also give them a few options - you know all of those bomb games?  the best student in class could take over your role and sit at the computer - call out the students). 

On top of all that, introduce students a bunch of games which never fail.  Guess the celebrity (they have to use english questions - and you have to prepare celebrity picture cards), Go Fish, and Scrabble - students love all of these and they are all student-centered - where you barely even have to pay any attention (you'll have to give them a dictionary when playing scrabble, so they don't bother you with question 'is this a real word?').

Question - why did they sign up for an English after-school class if they had no interest in learning/playing English games?

I don't know about OP's school, but at least at mine, the students didn't have a choice. At least she has all one grade, mine has all three grades combined (boys and girls), and I'm still by myself. The boys sleep through it and  the girls talk through it or do homework for another class. I understand OP's pain.

For me, it's worked really well to have and enforce some basic rules. (These are the same rules I use during normal class). I have a Class Dojo account that keeps track of points for me and I just use the phone app during class to award points to students who are following the rules. For every 5 points they get a raffle ticket and I draw about 5 names at the end of class to choose a prize. I give students three warnings, and after that they aren't eligible to win the raffle. It's usually candy only prizes, but I throw in makeup samples and other free stuff I've gotten as "service" and don't want. Occasionally I'll make cookies, or buy a few notebooks. I hate spending my own money, but I think it's well worth it as I've seen a great improvement in the students behavior since last year.

One thing I have been trying to do is project based learning. Last year I had them learn about the US State I am from. Each group put together a part, and then they put all the parts together in a presentation. (I divided into sections like: famous places, culture, school life, famous people, basic facts (climate, weather, flag, etc.) and history). After this I had them do the same but teach me about Korea. (Korea first might have been easier). Then they chose their own country and did mini presentations in front of the class. They still did whatever they wanted most of the time, but at least they learned some English too.

This year I asked them what kind of English club activities they wanted and then took their ideas for lessons. For two months we had an English soccer club--I let them play soccer as normal and awarded bonus points if they used any of the expressions I taught them. We did the same for a board game club. Now we are having a movie club. Basically I have them watch Mr. Bean videos and then write and role play their own dialog. They like watching the movies, but hate doing the other stuff, so I will probably change this soon.

Anyway, I'm following the thread for ideas. I wish you the best of luck with your classes.