It means that, the woodern platform has so much restriction I can't fix it on top of the stair to create a floor, unless I am missing something
Ah, try to edit the stairs to be talller, longer, potentially wider (if desired) instead of two pairs of stairs (although possible)
You'd want a bigger surface area I reckon to fit the platform on there.
In the worst case, if you get it to place a neat platform and dislike the stairs still, you could then still replace the stairs and edit them to your liking - but it shouldn't be that difficult. (remember to have your cursor further to the back end of the stairs top "space" (not the step) to further shove the platform back)
To later on expand when you have the first platform set how you'd like it,if you then hover to the corners of the platform at times they'll snap in place correctly (other platforms, that is)
To edit stairs, ctrl+click them, or press E near them, and an "edit" button should appear, with which you can change witdh/length/height