I think 40 per mile is bit on the high side.
I ragree with amaferanga's post. In a chaingang training ride my HRM usually come sout with about 1300 burnt in about 1h45 over a 60km circuit. That's with me doing my share of the tack. Road races are probably a bit more intensive because they're jumpier (but still the calorie burn will be about the same).
Alot can affect the amount of calories you burn and that info can't always be put into a machine. I had a medical at work which indicated that I had very low fat and high muscle mass (significantly outside the normal ranges). This means I burn calories faster even at a standstill than most people, something the HRM can't tell just from the height/weight measurement.
Anyway, keep riding, enjoy it. That's the key - for all the numbers we follow, we ride bikes because it's great and good news on the weight loss, I'm sure there's more to come.