Actually, if you can continue working and keeping yourself busy, I would say go for it. There is nothing more grounding than work. Also, since you work only 2 days, it's a nice balance between retirement and keeping busy.
Can you explain some more why
"to concentrate on my job become each day more and more difficult"One reason could be you are not interested in it any more, if that is the case, then yeah letting this job go is fine... you have done your share of "working". If it is because you cannot keep things straight, use external tools like diaries, reminders, notes, chimes, bells, whistles.
It is hard to be present at times when the energy is pulling us around, it is just a matter of training ourselves to come back here to what we are doing, again and again.
Hope this helps!
Wish you a wonderful (semi) retired life!!!!!