Samrawit,
Everything should point first and foremost to your skills and your services, such that mentioning your graduate degree in the first sentence would sound more appropriate if you said, "My graduate degree in Social Psychology makes me a better proofreader and editor." As it is, while it is clearly a bonus to have an advanced degree, it isn't that clear why you mention it.
There's a book from the old days about job hunting called "Jobs for English Majors and Other Smart People." The premise of this book was that smart people can do many different things. So, there's no question that your education will help your freelancing goals, but you still have to spell it out for clients who may not get the idea intuitively.
That said, you later wrote, "As a proofreader and copy editor, believe that every written content deserves scrutiny."
First, this sentence is missing a subject, so that's a very glaring mistake. Second, what you believe doesn't really matter that much. As a proofreader, it's understood that you believe in gramatical scrutiny, but more important than that, your clients are less interested in your beliefs than in the results you can give them.
Instead of "As proofreader and copy editor, believe that every written content deserves scrutiny," what you should be saying is, "As proofreader and copy editor, I can find and fix content and technical errors that stand in the way of your having a completely error-free manuscript."
Do you see the difference? It's not your belief that's important, it's what results you can achieve.
So, make sure your write-up is completely error-free, then focus on the results you can deliver. Then, try to allign everything you say with your ability to provide excellent services. "My college education shows that I am doggedly attentive to details, which allows me to turn a rough draft into a polished manuscript."
Certainly, your write-up is not bad ... but it might be helped with these tweaks. In addition, look very, very carefully for flaws in your own writing. If I can find them -- and I'm not particularly detail-oriented -- then anyone can.
Good luck.
