I'm sorry about the confusion you may be experiencing with the alignment of your image. The "Alignment" button that you were unable to find, is a button thats in a different editor we have which could be why you were having a hard time finding it. To be sure your image is inserted as large as it can go, you want to click on the blue arrow at the bottom right of the image (see image below), then click and drag the image until it can't stretch any larger.
Once that arrow is stretched as far as it can go, you will know that its at its maximum size. When sending yourself a test, the background of the email is going to have a white background so be sure that isn't what you are seeing when you receive your test email. Try seeing if your image is as large as it can be, and send yourself another test. Try sending a test to multiple email clients to see if maybe its just the email client displaying the email with the white on either side.
... View more