Will this cause damage to my Ford Fiesta ST?

Today I removed my scuttle plate on my car to remove a build up of leaves underneath. Before taking it off, the scuttle plate was touching the windscreen creating a kind of seal to stop water getting underneath it. This was quite tough to break the seal when removing the plate. Putting it back on however, the plate no longer touches the windscreen which allows water to now run underneath. The gap isn't very big but it looks like it needs some kind of seal to attach it back to the windscreen.

I just want to know if water runs underneath will this cause any damage? The windscreen edge is still sealed, but water can now run underneath the scuttle plate. Any ideas how to reveal it? I have a mk6 Ford Fiesta ST500, 2008 reg.

The windscreen is bonded to the car. The part you describe is a cosmetic item.
It's possible that water may collect under it and eventually lead to rust. But it's the seal between the glass and the frame that is waterproof. You could always squidge some clear sealant into the gap. A good weatherproof silicone should do the trick.