How are chromosomes counted at the end of mitosis in a plant cell?
I think I know what is confusing you.
A chromosome can have one or two chromatids. If you have two chromatids, you don't necessarily have two chromosomes. This is what happens during S-phase, during replication. Before the S-phase each chromosome had one chromatid, after the replication, it has two. So the number of chromosomes stays the same.

In the karyogram (the picture with all chromosomes), each object is one chromosome. Usually those will be double-chromatid chromosomes, and you will see a nick (like here). After these chromosomes divide, you get two separate objects → two identical chromosomes.