B4: The Lost City is a classic module for D&D. At one point it (in)famously stops giving full description of the rooms but instead lists monsters in each area and tells the DM to figure out why they’re here themselves. Once the reprint will show up in new anthology, I’m sure people who complain online whenever WotC uses “ruling not rules” or “DM decides” or “these parts were left for the DM to fill in” in their design (and then continues buying WotC books to keep removed and doesn’t touch 3rd party or other games for some reason) is going to be normal about it. /s
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.