YouTube uses a 16:9 player, so it is what it is with regard to 4:3 uploads to YouTube.
Please review the YouTube document on this type of matter
After you read that document, any questions or need clarification, please do not hesitate to ask.
Add On...if I need to get into version/computer specifics, please post what version of Premiere Elements that you are using
and on what computer operating system it is running.