Bad Lessons Happens to Everybody
We all have had lessons that fall flat or aren't engaging or they may be good, but a class doesn't get into the activity. This happens. Accept it and move onto the next thing.
Know When To Abandon an Idea
When you sense that a lesson isn't working or the students aren't engaged, there are a couple things you can do. First, if it's unsalvageable, as Kenny Rogers says, "You've got to know when to fold 'em." The key is how you handle it, and if you handle this situation with control, your students will feel that control, and you can work with them, and this situation can turn into a positive.
Brainstorm with your students.
One thing you could do to turn a bad lesson into a good lesson is to brainstorm with your class. You could teach ways to give suggestions and elicit suggestions from your students that could have turned your "bad idea" into a "good idea". You might be surprised what students will come into, and on top of that, they are learning and using real natural language.
Have more time.