I hurt my girlfriend two days back. Now she just wants to be friends. As a friend, how should I get her back?

Friends respect each other's wishes. If your girlfriend doesn't want to date you, don't push her. Give it time to let her cool off. After awhile, give a very brief but heartfelt apology for hurting her, and assure her that you'll respect her boundaries, including her decision to just be friends. Then be a good friend to her, or let the two of you drift apart. If she changes her mind, she'll say she'd like to try again. Otherwise, it may be time to look for a new girlfriend. There's no way to make her want you, so the best you can do is respect her wishes and keep being the best person you can be.