2518 is described in Scott as Perf 13.25 x 12.5 (which this is).
2519 is described as a self-adhesive booklet stamp but with no perf structure given.
The perfs look to be classic "serpentine" which leads me to default to this as 2519, but I don't know if there is something else I should be looking for.
Unitrade lists 2518 as having limited distribution (in Keepsake Folders) and indicates the perforations are 13.1x12.5 and are not serpentine. Number 2519 is indeed serpentine and is listed as 13.4 all the way around. It seems therefore that you should have #2519, but it also seems you need to get that perf gauge out again and re-check the perforations.