The kiln wash will do it’s
The kiln wash will do it’s job at that temp – which is to say it will prevent your glass from sticking to the kiln shelf.
That said, you will likely get some kiln wash peeling off the shelf and sticking to the glass. That isn’t a problem though – when the class fully cools just soak it in vinegar for about 20 minutes and the kiln wash will come right off with a soft brush.
You will need to scrape and re-kiln wash the shelf.
Helios Kiln Glass Studio