If memory serves the string should be approximately 31/2″ shorter than the bow so you should be about right, just measure the string to ensure it was not labelled wrongly. Probably as well to measure the bow just in case that is marked up wrong.
I think the maximum recommended number of turns in a string is about 20 so wind her right up in 5 turn increments and see if this helps.
Failing that lets hope someone else has some recommendations.
Mark.