I'm guessing you used up fuel so your ship became lighter, which increased your jump range.Too bad the OP had to take the self destruct.
One of the suggestions made actually DOES work: I have successfully jumped a distance beyond what my FSD is capable by heading toward the target system in supercruise until I've closed the distance gap. Once the target system is within your jump range you can make the jump. It does take hours of flying at 2,001c but it can be done.