Before I talk about why there are still 46 chromosomes, I'll just review the basic chromosome structure. Each chromosome has a chromatid, with one centromere in the middle.
Chromosomes aren't counted by how many chromatids there are, but rather how many centromeres. When DNA duplicates, the chromatids replicate themselves, so each chromosome ends up having two sister chromatids joined at the same centromere.
There is the same number of centromeres in the cell, so there are still technically 46 chromosomes. However, there are 92 chromatids.
This used to be confusing for me too :) hope it helps!