For a first attempt this wasn't bad. However that doesn't mean it's good either. You have pacing problems throughout, with the story seeming to jump between certain points, skipping the stuff inbetween, and then the giantess herself jumps a bit, acting kind in one instance, and then suddenly getting cruel, with not really anything to mark the change. It's still better than some for a first attempt, and I suggest you keep writting, as there's a lot of potential here.