Oh, sorry - I thought you were doing A levels - I didn't read your thread title carefully enough. Bad RC.
You were talking about organelles replicating, and I thought you were getting confused with the circular DNA found in organelles, and the chromosomal DNA found in the cellular nucleus. That's A level stuff, so you don't need to worry about it at your stage.
Have you heard of the haploid number? A normal somatic (body) cell is diploid (2n) which, in humans, is 46 chromosomes. Just before mitosis, the cell duplicates its cellular DNA, leading to a 4n state, or 92 chromosomes - so you are correct. We don't often talk about this stage, so remember than after mitotic division and division of the cell into two daughter cells the number comes back down to 2n, or 46 chromosomes.
Does that make sense?