You could use sprintf:
$list=sprintf("%-10s %-30s %d\n", $sec, $title, $seats);
Of course, you would need to adjust the widths of the fields according to the expected maximum lengths of the data. You should also use appropriate format types (I assumed here that $secv and $title are strings, and $seats is an integer. Different format specifiers may output the same values in different form).
Side question: why do you copy $sec, $title and $seats to different variables? Unless you are doing something else that your snippet didn't show, it doesn't make much sense.