Hope you didn't put too much on

Back all does what it says on the tin - backs all at the odds you state. Never seen the point in back all myself as I doubt many ,if any, people use it.
You'll need to set up some excell triggers if you want to back only one horse at 1.05. There's a program out there called discombobulator ? that I think my do what you're looking for and it's free have a look at
http://www.gubbed.com/betbot.html ,
nb Gary delete this if needed as I'm not connected with the prog , don't use it, or think it's in competition with yours.