A few words about ironing.
Ironing is a really important part of the quilting process. Before you start cutting anything, you should iron your fabric. It will really make your life much easier down the road. And then, after you piece a seam, like this, when we have one pieced here, you really do need to iron it.
Some people think finger-pressing is enough, but personally, I don't. I go to the iron just about after every, single seam. So you can use your iron with steam or without steam, and the first thing you should do is set your seam by pressing it closed. Then, normally, you would press your seam to the darker fabric. Here, they're both sort of medium. It doesn't really matter, but I would press it toward the larger piece.
You don't really ever want to press your seam open, because it's just not as strong a seam, so closed is the way to do it, and you just sort of slide it over the edge a little bit. Don't stretch it. More of a up-and-down motion than a vigorous sideways thing. Turn it over, and here's where you want to make sure that the seam is fully open. Sometimes, it bends, it gets, you press it an it's not open, and then your block isn't big enough and that is the reason why. So.
And that's a really nice pressed seam.