Your email address most likely did not send the spam email. If you hover your mouse over the address purporting to be yours it will reveal the actual address that sent it. You can also check the senders address by ticking the box to the left of the email in your list of emails then go to "More" in the menu bar and select "view source".
Your email address will have been harvested by spammers and they will be "spoofing" spam email with your email address to make it appear to be from a genuine person.
It may be that the spammer has got your email address from a compromised email account which had your address in its contact list or indeed your email account has been compromised.
There is nothing you can do regarding the email account being spoofed other than to advise all your contacts to be wary of any emails coming from that address or it may be best if you stop using that email address and inform all your contacts that your email address has been compromised and they should delete any future emails from that address.
See link about spoofing.
Email spoofing - Wikipedia
