HI Jenny,
Congrats on shopping for a nice new bike!
Hey you've been riding for 5 years so you won't be a 'goober' even if you try.
Remember it's YOUR money and YOUR test rides, so just wear whatever you'll be comfy riding in. People wear both full biking 'kit' and plain street clothes into bike stores all the time.
My advice is to not worry what the bike store employees think of you. They should be worried about what you think of them!
Go for it and HAVE FUN shopping around.