Forcing a woman to have sex is rape, plain and simple. And, regardless of every other consideration, is a crime which, if your sister had gone to the police, would result in a prison sentence if you were convicted. That was a despicable act that you perpetrated.
Now your sister is cooperating with you, and if you are telling the truth, is as eager as you to continue this clandestine relationship. As I've said, I'm not interested in trying to moralise, as you and your sister have made your choices and decided that your sexual desires outweigh any other considerations.
Even guilt hasn't stopped the pair of you, and the more the two of you do this, the less guilt you'll feel. The risks of capture is real, and the consequences are incalculable if you and sis are discovered. Furthermore, what do you want in the long-term? I do know a brother and sister that live as husband and wife (and only their closest friends know the truth), with two perfectly normal healthy daughters, but they've been deeply in love with each other from childhood. The fact that you started out by raping your sister doesn't suggest much love to me!!!
oh two have to decide what you want, it's no good asking us. The law is clear enough, and you're breaking it. But people break the law all the time, or the world's prisons would be empty. We all live with our conscience, and make decisions accordingly, and sometimes doing as your conscience guides you can put you at odds with both social opinions, and your country's penal code.