The idea of shh/pat is to calm and relax your baby. WIth such a young one, hold him against your chest and do shh/pat until he is relaxed instead of rocking him. Make sure you are firm with the pat and the shh is fairly loud. Then when he is calm and his breathing is deepening put him in the cot and continue until he is asleep. If he cries, pick him up and do the shh/pat with him against your chest again until relaxed, then put him down again continuing the ssh/pat and just repeat the cycle until he goes off. Check on his awake time and try to get him upstairs a little before he is really tired so he does not get overtired and it should be a lot easier.
Are you doing a wind down ritual?
Hope this helps