Roller shutter guides too short?

Here are the examples from the RAL guideline. According to this, both variants are permissible. For absolute darkness, either the guide rail or the end piece would probably have had to be notched out. Regardless of light tightness, attention must be paid to whether the end pieces are drip-proof. If not, a second water-conducting level must be created under the windowsill. One would probably have had to commission absolute light tightness in order to have a claim to it.

I just checked again and also closed the blind. For us, it is exactly as suspected. However, since there is significantly less distance between the shutter and the window for us, the glow of light is naturally much less. Moreover, for us, the windowsill connection profile is a side U. Yours looks more like an L.

For absolute darkness, either the guide rail or the end piece would probably have to be notched out.

As I have already noted, the OP does not have ETICS and therefore no sliding piece that could be notched out. They should simply have left/made the guide rail longer.

With us, everything is also "short". Still totally dense and dark.