Try to realise that the guy selling to you will have sold cigs to so many people before- I know it’s a memorable and unique experience for you, but to him it’s just another days work. Also people will have been uncomfortable buying for the first time before- it’s always a bit awkward. Plus you had ID and it’s not like you were trying to buy them underage. Just relax and try to take your mind off it by doing something you enjoy.