Sealing/waterproofing drop in bed liner F150 question
 

We bought a new F-150 super crew cab recently and I had the dealer install the drop in bed liner. I then went to a third-party truck accessories shop and had them install the Low Pro Q soft tonneau cover. Everything is great, except I learned that the dealer cut the bed a little short width-wise at the cab side part of the bed liner where it meets the sides in the top corners. The gap is only 1/2" wide probably, but when it rains, it trickles in here and will get wet inside the bed. It seems all else is weatherproof.
The dealer said they can't do anything about it and their other lot bed liners are like this. Likely excuse. I tried using silicon to plug this gap, but it didn't work and fell out/melted (it could have been old silicon).
Does anyone have any other suggestions? Foam or maybe new silicon will work better? I can attach a pic if it helps.

Thanks!

If you could, go ahead and attach a pic because I'm having a tough time understanding the issue.

Thanks, and welcome!

Here are some pictures of the gap. It's not big, but enough to drip water down in there and get stuff wet.
The silicone mess in there is the old caulk that didn't hold.

Thanks!