Firstly, your teaching method is wrong. Your puppy will learn faster & happier by praising them, when they pee at the right spot, make sure you praise them a looo000OOOt!!! Or perhaps u can give him treats. Dogs love to do what their owners like them to do, they love to be praised, so if you beat your pup when he pee, he will only think that it is wrong to pee in front of you, so he will wait u r not there & pee. Since he doesnt understand human language, u need to show him what you like by praising.

Secondly, you said you just bring the pup back & the fact that it is just still a pup, he needs time to get use to the environment, & since he is a pup, he cant hold the bladder for long, so you must accept accidents do happen.

To me, your pup considered achieve great achievements already, so fast already understand where to pee, but remember for a pup understand is real smart already, if they miss sometimes, you should forgive them.