you did nothing wrong that is the way the plant grows. you could try cutting off the flower heads and see if they re-leaf. they are easy to grow from seed. personally I'd buy a new pot.
welcome to GoY too :o)

And next time, keep an eye on it and nip out flowering shoots, which should extend the life of the leafy parts.

It seems you're not harvesting it much - my parsley plants never get the chance to flower, lol!

Just cut it back to some fresh, new growth and (if it's in a pot), repot into some fresh compost and keep it out of the sun if possible. It'll take ages to regrow to a decent size, so consider getting another plant to tide you over.