What skill was that, not mixing enough water so it did not self level. You
should not have had to trowel it.

In any case, it won't be easy to get it up, its going to want to rip off the
face of the plywood if you try to chip it.. Your best bet is make what you
did work. What is the problem? Maybe a little hand grinding with a
concrete brick will smooth it enough for your needs, a brick can be used
like sandpaper on cement surfaces.

If I had to remove all or most of it, I might try a drum sander with a very
corse grit (60 or corser). If it were thick, you can rent a concrete
grinder but that sounds to be overkill for what you describe. A belt sander
with similarly corse and strong belt can be used to touch up an otherwise
uneven trowling job. An orbital pad sander (large used for refinishing
floors) might pass depending on the condition you have and need.

I followed the directions to a T... 2 parts cement, 1 part water. A
colleague who suggested this to begin with stated not to make a lot at
one time as it will harden up rather quickly. I followed his directions
by doing just that, taking a roughly 20 oz. can and put in a bucket,
two of those and one of water.

I spoke with him this morning and he noted that I may be able to use a
brick to sand it down smooth and perhaps use another mix that is
premade to even out other areas.

We shall see.

Thank you all for your suggestions so far.