The last two weeks of the challenge are a great time to touch base again with your entire network. If you haven't yet hit your goal, let your contacts know how close you are to it. Provide them with a breakdown of what it will take to get there. For example, "If X number of people contribute $X apiece, I will achieve my goal!" If you've already succeeded in achieving your initial goal, increase it. People love to be the ones who help get a fundraiser to the goal line!
Create a sense of urgency using the last day of the challenge (April 18) as a deadline. Circle back to those folks who perhaps offered to support you but have not yet contributed. Folks are busy, so a slight nudge is always appreciated! And don't forget to ask your contacts if their employers match their giving. It's a great way to have donations doubled and sometimes tripled!