I doubt you'd have had much problem adding a few noughts on and getting matched but Cheltenham isn't a normal meeting, probably trading t least 5 times normal amounts. Even if you managed to get matched when you add a few noughts to your stake you'll behave differently even if the market doesn't, it's easy to let things run when there's only a tenner at risk you become a bit more cautious when there's a thousand if you aren't used to it.
I'd say completely ignore how Cheltenham went and get stuck into a normal bread and butter Saturday like today as that'll be much more representative of what yoou'll have to face day in/day out.