Well, you need to come up with a central region that consists of unstrained electrode extensions and a strained scattering region. I suggest you first create two unstrained ribbons (to be used as electrodes) and then a strained ribbon for the scattering region. Then somehow interface these three building blocks, perhaps with some geometry optimization. Right now, you have a few hydrogen atoms in the middle of the structure that almost overlap - these will surely move away from each other during geometry optimization.