If I were you, once the boat was back far enough that you had 3 or more feet of clearance between the bow and the piling, I would put port in forward and starboard in reverse, swinging the stern to port and the bow to starboard -- with a fender held between the bow and the dock. That way you you will have better leverage against the dock than you have using your swim platform (which is probably not built to handle that load and certainly has less leverage).
This is how we almost always leave a dock with open water on one side. We add the element of a line from the bow to the dock, around a cleat or bullrail, and back to the boat where it is held by the person not driving, who is also holding a big fender between the bow and the dock.. The driver puts the rudders hard over into the dock, the dockside prop in reverse and the outboard prop in forward.
The combined prop walk of both props turning in the same direction and the outboard propwash against its rudder move the stern out very quickly. The line to the dock keeps the boat from moving forward or aft, and the fender keeps the side of the bow off the dock. If we're doing this against a strong wind we simply use more power, particularly on the outboard engine.
We pivot the boat out at least 45 degrees or even more if it's windy and there's a boat on the dock behind us. When the boat is angled out the way we want it, the rudders are centered, the dockside transmission goes to neutral and then reverse, the person on the bow lets the bitter end of the bow line go and pulls the line back around the cleat or bullrail and onto the boat as the boat backs smartly away from the dock.
Depending on the direction we want to depart the area we either continue backing the boat in a turn until we're headed parallel to the dock or we continue backing out at an angle until we're far enough out to engage forward and turn away from the dock in that direction.
This has become our standard method of departure from a dock unless the wind simply pushes us off it.. No pushing the boat out from the dock, no putting the swimstep against the dock, no assistance from the dock needed at all.
PS--- This technique is much easier to do than it is to describe.