I wasn't a good DM either. But then I learned. I threw encounters at the players I thought might be fun, and I missed the mark almost every single time. But my players had fun, so I don't see the problem in getting those encounters wrong. And every failure taught me so much more than every success.
If you fail, but you keep it fun and learn for the future, what have you lost? Only your pride.
Is there an issue with these sites I'm not aware of?