I had this happen to me as well. I called the Humira folks at their 1-800 number and they have nurses on staff that you can talk to and they can advise you based on a bunch of questions they ask you. I had to reinject myself twice, but they told me not to bother the one other time it spilled.
It's easier to reach Humira then it is to get a hold of my own doctor, especially at this time of the year!