I don't know how to approach or talk to girls

Today, I saw a very pretty girl. Many people have told me that you should just approach and talk to someone if you really like them. After gathering a lot of courage, I went straight up to her, said Hi, and asked, Are you from so n so college? She answered very politely, No, and told me the name of her college. I replied, Are you sure? Because I thought I saw you there (even though I hadn't). She said No again, so I asked for her name and told her mine. She repeated my name and said, Hi [My Name]. And oh man, right after that, I completely forgot my script! I just said Bye and walked away. 😭