The problem is that when the formula searches for the first chr(13), it doesn't take into account where the FOLLOWUPS: string is located. It needs to be modified so that it starts searching for the chr(13) after Followups. Thus, you need to embed the Instr() function within another Instr() function. I cleaned up the code by adding a variable. (I might be missing a parentheses, but I think its okay).
NumberVar FollowUpsLoc;
FollowUpsLoc := Instr({table.fieldname}, 'FOLLOWUPS:');
IF FollowUpsLoc > 0 then
Mid ({Table.FieldName} , Instr(FollowUpsLoc, {Table.FieldName} ,chr(13))+1)