I'm really confused as to how I fill out form 1040NR-EZ. I know that the UK and the US has a tax treaty but I'm not sure how it works.

I am an F1 student in VA and I earned about $4200 in the tax year. Will I get all of the federal tax back?

This is from publication 901. Tax treaties:
A student or business apprentice who is a resident of the United Kingdom immediately before visiting the United States and is in the United States for the purpose of full-time education at a recognized educational institution or full-time training is exempt from U.S. income tax on amounts received from abroad for the individual's maintenance, education, or training.

So tax treaty does not provide any deduction. You will get exemption of $3650 and itemized deductions. Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents