I think your pub is good. It does not matter if you are the senior author of the paper (but you need to show that you made big contributions to the paper).
You need to satify at least two of the following issues for EB1B (or Eb1A).
Did you serve as a judge on graduate committees, judging other's work, for example, reviewing papers and proposal?
Have you joined any associations?
Have you won any national or international awards (student awards and proposal awards do not count)?