Nope. It is not risky at all.
I never did commerce and I do Legal Studies and Business Studies. I'm not sure exactly how Economics works out, but in Legal Studies and Business Studies, you'll learn the stuff anyways so you don't really need to have any background in Commerce. During the first few lessons in legal, I was like O_O because I didn't understand any of the terminology, but I'm sure your teacher will be helpful and you have many resources which can help, so learning the terminology will be a breeze ^__^ I know some people in my Legal Studies class who never did Commerce and are basically topping the class and beating the students who have done commerce. I think this girl who ranked 1st in Legal Studies never did commerce at all :O
You shouldn't have to worry about anything. Basically the only subjects you would need previous knowledge for would be maths and english (I think), other than that just choose subjects based on what you like. You'll learn what you need to learn in your Legal Studies/Economics class.