What do you mean "I filled out a W-2?" Employers issue W-2's--you do not "fill out" a W-2 for yourself.
If the "less than $400" that you made on the website was your only income you do not need to file a tax return.
Or did you have other income? Is that what you mean when you mention a W-2? Did you receive a W-2 from an employer?
When signing up for the website, you are instructed to fill out a W-2 form as a sole proprietor. The less than 400 dollars is the only income I've made from the site. They are not considered an employer.