Stamp Left or Right?

Sent off my Mother's Day letter yesterday which I was pleased to hear arrived this morning. It dawned on me while writing it up, I have never addressed a letter before. I even had to Google which side of the envelope the stamp needs to go on. Then after I put it in the postbox I saw that I may have filled the address line in poorly and most likely in the wrong spot. Hopefully the post sorters thought a cute 4 year old did it rather than a big old student. Posting and writing letters. Day of firsts I guess.