Dont worry about it hun , he will eventually get what you're asking him to do ... just be lavish with the praise (and maybe a treat) when he gets it right , and ignore any mistakes he makes
at 4 and a half months your pup is still just a baby really , Toffee was about 6 months old before we stopped having any accidents at all in the house , and about 7 months old before he started 'going' on his walks and not holding it in until he got back into the garden

__________________