So that's not the best way to make a 1 time use command.. Here, use this one instead:
command /start:
trigger:
if {start::%player's uuid%} isn't set:
give player white concrete named "&f&lSugar Generator"
set {start::%player's uuid%} to now
stop
else:
send "&b&lBakedGens &7You already have a plot!"
So what that does it, when they execute /start, it sets a variable to when they did it so if you ever want to get how long they have been playing the server, you can (Placeholders/skript expression works aswell).