My first was 1 day over, and 6lb14oz, and my second was 6 days early, 7lb10oz.
Is your cycle longer than 28 days? If so, that might bump you a few days later. Doctors usually count on a 28 day cycle when they calculate due dates. Your ultrasound would give a pretty accurate date, though.
Maybe try some of the other suggestions - raspberry leaf tea, evening primose oil, etc. I think there is an article on labour stimulation somewhere here on BellyBelly.
All the best!