Here are genuine stamps perf. and imperf.:

Some cancellations are genuine postal useage (e.g. 2 skilding) and some (e.g. 4 skilding) are post-dated. Here are Spiro fakes/forgeries (call them what you will):

The issue has been extensively forged, and your canceller indicates a forgery, I'm afraid. This kind of canceller was not used in Iceland. Here's an extract from Facit showing the types of cancellers in use at the time.

The skilding issues have contemporary cancels of types D1, D2 or A. Post-dated cancels are typically type G. Genuine roundel cancels such as yours all had a numeral in to indicate the post-office location. Later, these cancels became the more familiar Type N cancel. Hope this helps.