No, it means that $UsnJrnl occupies 2576 clusters on disk. Sparse clusters don't occupy any space on disk, if you'd try to read sparse cluster, e.g. cluster 10 in your example, NTFS just returns zeros.
Generally, you can't determine start and end cluster of the file, since files can be fragmented - your example says that first 1408 clusters are not allocated on disk at all, then 128 clusters of that file occupy disk clusters 510119 - 510247, then 2448 clusters of the file occupy disk clusters 256 - 2704; so in this case you can't say that file begins by cluster X (on disk) and ends by cluster Y (on disk) - it's possible only if file is not fragmented (when it uses only one cluster run).