I can relate to that feeling of "creating resentments for the sake of having something to put down".
There were times when I went into the 4th step with some expectation of what was going to be on the other end - what my inventory would look like. I got drunk each time I approached a fourth step with that mind set.
Specifically, here is how my last 'first' fourth step went:
I wrote a prayer asking that I be show what I need to see at the top of a piece of paper.
I wrote down ANY name that came to mind (or principle/institution). At some point names starting coming to mind that I hadn't thought of in years - or people who I had very brief encounters with. So, I had a list of names, institutions and principles.
Next - I wrote each name on the left hand side of a new piece of paper, and wrote the same prayer on the top of the page. Then I wrote down all the bad things they had done to me, or things they did that bothered me, I didn't agree with etc.
This could be as simple as "Phil - Sucks up to the boss and work. Flaunts his achievements. Doesn't say "god bless" when I sneeze.
Of course, there are also those things people did that really hurt me. "She cheated on me" - Regardless, I write them all down.
That is my resentment list - and with a mind set that I will be shown everything I need to be shown if I just give it the proper attention, it can't be argued with.
Resentments, at the phase you are currently working - isn't about what harm you have done to other people. It's about all the bad things that have happened to you. Be very selfish here, don't hold back..even minor irritations from years ago should be written down. It's a process and I think you will be amazed by the time you get to the part where you were "wrong" or caused harm to another.