A full screen option has been enabled in the new Gmail compose experience. If you do not see this yet, it will probably roll out to you on August 6th, 2013. To try it out:
1. Click Compose.
2. Click the double-arrow icon at the top right of the compose window.
3. Enjoy a larger composition mode that displays all of the formatting options by default.
If you want to make this option your default view, click into the options menu at the bottom right corner of compose and choose “Default to full-screen.” The next time you click Compose, you’ll be sent to this mode. Both types of compose can be minimized by clicking the black bar at the top.
On small laptop screens, the new Compose experience made email in the lower right to small and difficult to read. For you small screen owners and others that want to put a new email front and center, enjoy the larger compose email options.