1.Say sorry really loudly.
2.Finish as much homework as possible. Make it look like you tried to do it.
3.Tell the teacher that you emailed it into school, but weren't sure about how attachments work. You must however, send your teacher an email, and attach a document with nonsensical random symbols, etc. for this one to work.
4.If your teacher appreciates honesty go to him/her as soon as the class starts. Act maturely and tell them that you fully understand the importance of the homework but were unable to have it done before class. Your mature behavior will make the teacher think you had more important things to do. Rather then tell them about what you were doing the day before just let them guess.
5.Say you honestly didn't understand it and attempted to come in for help, but couldn't find her. (If asked what time, make sure you know a reasonable time when she is likely to leave.) Lastly, put the blame on him or her by saying you did indeed turn it in and act extremely aggravated by their loss of your work, (this must be accompanied by an eye-opening shocked look followed by a deep frown) This, last one takes scruples, however, because it might change the teacher's opinion of you in the long term, but it does have a moderate chance to get excused.