I agree with those who point out the time limit, but as a die hard ttc'er for the last year if this had been my test I'd have been jumping for hope and asking all my friends if that was a line too.

You'll have to decide for yourself, but for peace of mind if it were me I'd wait a couple days and try again to make sure. (since I assume you don't want to be pregnant based on the fact that you say you have an IUD.) I hope it turns out however you are hoping it will.