You must have had a lousy driving instructor!
First all, he should have taught you that you should always 'assume the worst'. If you're approaching a blind bend you must assume that there's a horse-rider, broken down vehicle or other obstruction immediately around the corner, and drive accordingly. If there are schoolchildren on the footpath you must assume that one of them will run out into the road, and drive accordingly. If it has been raining recently (or is still doing so), you must assume that the road will be slippery, and drive accordingly.
Secondly,your account of the accident suggests that your foot was still on the brake pedal while you were actually entering the bend. Your driving instructor should have taught you that you should have fully completed braking before you even start to turn the wheel.
The test for a successful prosecution of 'careless driving' is whether the defendant's driving fell 'below the standard expected of a competent and careful driver'. Your driving clearly did so. Plead guilty.
Chris