Yes, generally REMAIN is not necessary to be used with AFTER. It is necessary when, depending on player choices in the game, you want to stop the execution of AFTER subroutine.
Imagine for example that (for your game) you give 30 seconds to the player to make his choice. For this, you can use AFTER, and after 30 seconds print <you lose!>. In this case, AFTER has to be disabled by REMAIN in most cases, in which the player has made the choice before 30 seconds. If it is not, then <You lose> will appear in the next turn
Another problem i had has to do with where the program goes after calling the AFTER subroutine, as it doesn't seem to go in the same line every time (as i wanted to send the execution back to the next turn). Using GOTO in the subroutine wasn't the best choice, because the end of the subroutine by RETURN will not be recognized. What i did is setting a variable to 1 in the AFTER subroutine, and then using IF/THEN commands in 2-3 lines in different places in the list i send the program back to the next turn. Hopefully, this works
Nice game in only 10 lines! Well done! Needing careful observing!