Dear 21 year old Amy,
Calm down. In seven years you won't care and it won't matter that your boyfriend didn't go to your birthday party. The bar scene is not his thing, it will never be his thing (be thankful) and you'll end up marrying him and having a beautiful life together.
Stop obsessing over every. little. thing. The future is unknown to you for a reason. Make the most of these college years. Join a sorority. Stay up all night. Call in sick to work to go to the beach. Be young! In just a year you'll have your so sought for "grown up" career job and you'll have to be conservative, responsible, and set a good example in all areas of your life. You'll never know who's watching or reporting your "scandalise" behavior. (You'll quickly learn the importance of this.) You never do anything crazy or inappropriate after you get your career job, there will just be people standing on the wings waiting to take you down. Stand strong. You're better than them and you know your true character.
Don't worry so much about getting married. Just live. Pour yourself into having a good time with Bill. In a few years he will put a ring on it and shortly after you'll have your own family. It will come. So stop obsessing.
Take better care of yourself. You have all the time in the world to make good eating choices and get your butt in the gym. For goodness sakes the school you go to offers one for free. Take advantage of the unlimited time you can spend getting lean and toned. It's not so easy later on and you'll feel better about your wedding pictures and your pregnancy later.
Enjoy your time working at Blockbuster. Even though you think it sucks now, you'll think fondly back on the friends you made and you'll miss those free rentals!
Continue to form bonds and relationships with your professors. They will be your biggest fan and advocate later on. They'll help you get jobs you never dreamed of and they'll push you to be an better educator. Don't skip their classes or half way do their assignments. You'll learn later, when the shoe is on the other foot, just how annoying, disrespectful, lazy, and uncommitted it will make you look.
Watch as much Sex and the City with your name twin as you can. Sleep in when time allows. Don't forget to spend quality time with your girlfriends. You'll need their love, support, advice and listening ears so make sure you're there for them in the same way.
Your family will endure a life changing event soon. Spend more time with your sister. Form a friendship with her and support her no matter what. She's going to need it, and even if she doesn't seem to appreciate it, she will and your relationship later on will be better for it.
Relax. God is in control. You have a beautiful life, so live it and have no regrets!
Your 28 year old self