You could possibly put some wood there. Like attach few pieces of wooden board (or one bigger one) there -> bolt it to wall -> bolt tv mount on top of that.

Or instead of wooden board, use metal (like this). Mount it to wall from corners, so one hole in the middle will match current hole. Metal plate should help secure the current holes.

But really, I would maybe leave this to professional to prevent more fuck ups. Or just move it 10 cm higher and use mount with movable arm, so you could put the tv lower.

Edit: Or just use bigger screws.