https://i.stack.imgur.com/dXam5.jpg
I tried to follow the steps for the similar problem, but there's not enough explanation. It says -d1/2 = -13cm/2 . However, the problem for that says d3 is 13 and that d1 is 11. Why are they referring to d1 as if it were d3?
The solution is completely wrong, which is not surprising since the solution is "for a similar problem".
As d3, in your problem, is the dimension along the x axis, xcom=-d3/2, not -d1/2.
Moreover, also the computation for ycom is wrong given your problem, although it may be correct for another problem.
The only correct thing on that link is the formula. That's what you need to use.