Christians, it's ok to sin as long as I promise to repent afterwards, right?

I've always been told that as long as I ask for forgiveness, sincerely of course, I shall be absolved. Because I'm craving for all manner of wicked things, pleasurable things, but I don't want to upset God or go to hell later on. So, as long as I say a Hail Mary or two after having.. um... committing the sin, it's all good... yes?