Sounds like your doing a good job.

You can try different exercises for the same muscle to see which ones target the specific muscle the most if that’s what your into. On the other hand it’s good to do exercises that actually involve multiple muscles so that everything grows bit by bit simultaneously. That’s the bast case scenario IMO. Machines that work out a single muscle are nonsensical for 99% of people. Ok, if your a world class tennis player, you need extra strong specific hand muscles, but most of us aren’t so we don’t.

And it’s true what you say, sometimes a muscle starts hurting like hell two days after the actual workout so you think you didn’t do a good job when all of a sudden you have trouble sitting down 😄

Without going into the specific program you use because I’m not familiar with it, I’d say the most important thing is good technique and posture. All exercises’ are much easier if you don’t do them correctly (other muscles start helping out). So don’t pump reps like crazy. Do it a little slower but be mindful about the muscles that should be working out. And if you have correct technique all of the sudden it becomes much harder because intended muscles are activated.

Look on youtube for how to do workouts correctly and WRITE IT DOWN because you’ll forget. And before every exercise remind yourself about the correct posture.