your are missing how it works mate,

the backer 'stakes' his $6
you are making liability of $100.

out of your account $100 WILL be taken

1. when the horse loses $106 goes back into your account.
the result = +$6 only. less commision

2. If the horse wins you get back nothing
the result -$100 (no commison as you werent the winner of the match)

so you either win $6 less commision or lose $100. theres no other result other then these 2