I have planned my work for this half and it seems the work is not as complex as I thought. what should I do in this case? It seems that the work complexity is more subjective. Talking to my manager would make it obvious and I don't want to lose the points in performance cycle.
Trying to obfuscate the complexity of the project is a losing strategy. Even if you are able to successfully do this, "confusing" is not the word you want people to describe you / your work as. The best engineers make things as simple as possible, and they get credit for helping others (especially from more busy executives) understand the core complexity/challenge of their work.
I think a better strategy is to extend the scope of your work so it has more impact. I wouldn't seek out complexity, just focus on getting more users, more impact, etc.