not a teacher
It's not clear what you are trying to express with any of these examples. The most natural one is (2) and it has the sense of "I didn't make the thing complicated. I made it easy and straightforward".
For example: I thought up a puzzle for the boy but I didn't want him to waste too much time on it, so I made the thing simple.
I'm not sure that this is what you are trying to say.
Student or Learner