Thank you very much! Adding that and changing one small variable, I am on the right path. Thank you!!

For those that want to know, here is the final code that is working for me:
// Bingo Card Number Guess SYNTAX: !guess
on *:TEXT:!guess *:#mychannel:{
  if ($2 !isnum 0-25) return
  var %guess $int($2)
  msg $chan $nick Chose the Number $2 .
  write C:\PATH_TO_MIRC\text\bingoguess.txt < $+ $nick $+ > --- $int($2) ---