Biogen won't be open until Monday, they won't really give advice but I suspect they would send a replacement dose, and you would send the defective unit back.
In the meantime, if you are absolutely sure no medicine went into your body, I think you could try another Pen tonight. Or maybe there is a way to salvage the unused dose and inject manually.
Here is a link that gives you step by step directions and pictures and includes what to do when it goes wrong.
www.avonex.com/pdfs/guides/Autoinjector_PEN_IFU.pdf
Thank you, I think I will re-inject. I am confident the medicine wasn't delivered. I'll call Monday.