Don't expect to be consistent with Widow... Especially if you're not used to playing hitscan... For sure you can get better, but it will take time. For now, you'll have your good days and bad days. But don't get discouraged from playing her...
Also, if you're having a good day and can hit shots... It's a good idea to be a little bit more risky with your positioning. Flying sometimes just for the hell of it, and to see if you can get a quick pick or something for example