I would undo it, run it back through the soundboard hole, take a string end and stick it through the knot, pull the knot as tightly as I could around the string end, and then push it back up and wind it back on the peg. It’s not going to be in tune for a couple of weeks most likely anyway.
That knot can be difficult to keep knotted around the string tie.
Here’s a few tips to make it easier next time:
Before tying your knot, put the string through the eyelet from the top of the soundboard to the back. (This will only work if you have a pretty good amount of length to the replacement string.) Grab the loose end and tie an overhand knot http://en.wikipedia.org/wiki/Overhand_knot
and before closing it off, slip the string tie in.
Tighten the knot.
Then make a loop and slip it over the string tie so that it lies next to your first knot. Snug it up. I like to repeat this when the strings get to about .036″ and smaller.
Look at Figure 7 at the bottom of this article: http://www.harptech.com/Articles/Strings/Strings.html
Put some tension on your knot with your right hand and pull the string up to the tuning pin with your left. Let go of the knot when you get to the back of the soundboard. Maintain some tension while you negotiate levers/disks, anchor your string at the tuning pin and bring it up to pitch.
One useful tool for forcing a stuck knot out of the soundboard hole, is a large safety pin. Keep one with your other harp tools, just in case. You bend the pin apart so the closure part is in line with the point, so that you have a kind of a handle to hold onto. Put the point of the safety pin trom the front of the soundboard, into the hole; when it stops, that is where the knot has stuck. Push gently but firmly. You haven’t damaged your harp or the string “shoe” on the sounboard string strip
Audrey, here’s another little trick so you won’t need two sets of hands. Get some clothespins….the kind with the spring….good strong wooden ones. After you pull the string through the hole, pull it taut and then put a clothespin on it right at the soundboard to hold it tight until you can thread it through the pin at the top.