It is clear from the various comments and the bounty that we are missing the correct step size. I believe the correct step size is:
The quay. That is, a move in the shape of the quay on the map. This is equivalent to a long knight's move, 1 horizontal and 3 vertical or 1 vertical and 3 horizontal.
My reasoning is as follows:
1. The quay is never mentioned anywhere in the poem or elsewhere and is superfluous to the puzzle as it could simply be replaced with deep water if it were intended to be impassable.
2. The phrase in the poem “my unequal step" contains the letters necessary to produce "quay". This is tenuous but the question bears the anagram tag. Perhaps there is a larger anagram I am missing.
3. The quay could be considered an unequal step.
My attempts to use this step thus far:
Have been unsuccessful. Presumably we are looking for a step that provides a unique shortest path which will be used to decipher the rest of the puzzle. There are a couple ways in which the quay step could be interpreted. If we are not permitted to jump over deep water then we cannot progress after the third step. If we can jump over deep water, rocks, and hedges then there are multiple solutions that each require 8 steps.
An alternative and more complex step:
Perhaps we are intended to use two unequal steps, a quay and something else. The simplest would be a single adjacent move. I suppose this would resemble a limp by alternating small and large steps. It’s not obvious which step we should begin with, but I believe there is a uniquely shortest path starting with the small step as depicted below. Black dots indicate the position after the short step and red dots the position after the quay step: