Funny: I have recently designed a web app for a client with extremely similar layout. I didn't know of this designer or his work. Yet when I consult Dribbble, I find many identical designs.

So who owns the copyright? That's one question. To what extend will one pursue you? That's another.

It's well known that flat design with plenty of spacing and subtle background colors works. Nobody has a copyright on that. So go for it.

On the other hand, if you copy the icons, logos, illustrations or exact color scheme, you might face legal action more easily.

But it's silly and impossible to try to be 100% original. You can't be. There are design guidelines that are reused a lot because they just work. So don't worry too much, avoid copying unique designs like illustrations and go for it. You'll be a great "designer" too!