You're code is wrong because you're not using { } after the if ($nick == Bill), so only the /set command is related to the if, the rest is executed in order so the else follow the /msg, this is not possible, try :
Code:
on *:TEXT:.target:#team-tt:{
  msg # The current target for Team-TT is, %target $+ .
}
on *:TEXT:.settarget*:#team-tt:{
  if ($nick == Bill) { set %target $2- | msg $chan Target changed to " $+ %target $+ " $+ , you may now want to set the channel topic. }
else msg $chan you're not Bill.
}


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