Thank you all the replies!
I checked the drain plug every weekend and fortunately there was no leak at all.
I have a super organised workshop and all my tools have a exact position in order to eliminate missing tools and accidents (torx bit in engine cyl, microfibre towel in fan shroud etc..).
I always work per my own check lists and Volvo workshop manual.
But of course this is not my main job only a hobby and now i made a small mistake by applying double washers. Lesson learned.
Thanks again all answers helped me to sleep well after this thing.
