Dear Mrbond,
This is quite a common occurence. Many times, with initial , or first few times in sex, the penis doesnot get erect. Well this is called performance anxiety. Its nothing to be worried about, slowly once you gain experience in the act of sex your self confidence will increase and this wouldnt happen. Try to relax when this happens.. Read this link on the topic. https://lovematters.in/en/marriage/marriage-troubles/honeymoon-impotence...
All the best.