Firstly I would advise not doing horse races near to the off when you are starting out. Most of us that have been doing it a while will do this a fair bit as this is when the odds are usually best. However, this is also when the odds are moving fastest and as you have seen (I expect the odds were moving against you) when you are new to this you are taking a big risk, and taking risks is the biggest danger in the early stages. If your horse had lost your free bets would have been lost and you would have only have the original loss on the Qualifying Bet.
Secondly, on Betfair if you don't get a match you have a number of options 1) leave the bet and see if it gets matched (not possible in your situation), 2) take different odds - also not possible in your situation 3) set the option to keep it in-play (this option is available once you have placed the bet) - also not possible in your situation, 4) place the bet in-play - even though the race had started you can still place a bet - the odds will be moving fast and the odds may be better or worse than you wanted but it will still be possible to place one.
There are also other exchanges (Smarkets and Matchbook for instance) which you will start using a lot because their commission is a lot less than Betfair and this will be important if you are going to be doing MB properly.