You didn't do anything wrong Ian. The software expected you to deposit more money into it using the deposit function so you could cover the bet. Looking at the results over the years, losing runs of 8+ are actually quite common, so if you only have around £100 in your bank, I think you will come unstuck quite often.
I would just use the software when you can and not place the bets in advance, unless you are using the exchange function after a winner as the stake is normally £2 for the next couple of bets unless the odds are really low. I expect this isn't the advised thing to do.
Or just run two banks which is what I do and and stake a fixed % on one of them. I use 2.5%. This way you can have a much bigger starting bank with out worrying about losing it all in a very short period of time and you can stick all the bets on at the same time like a normal system.
Some people see things that are and ask, Why? Some people dream of things that never were and ask, Why not? Some people have to go to work and don't have time for all that ...
George Carlin