It appears to be genuine.
Thee are several types of forgeries of this issue, and most share some common mistakes.
1. The road markers immediately above the "S " and "I" should have six dots (though two of the four can be a little difficult to see sometimes). In most of the forgeries, they only have four.

2. The church should have a window, a steeple with horizontal lines, and windows in the lower building. The common forgeries are missing all of these features.
3. The road should have horizontal lines. With the forgeries, there are also vertical lines.
4. The perf should be 10.5. Common forgeries are perf 10.
5. The lines within the clouds also vary in the forgeries, but this can be difficult to spot without a side-by-side comparison.
Looking at your stamp, 1-3 indicate that it's original. Check the perfs.
