Could an abdominal ultrasound at 8 weeks be off by a month (month further along)? fetus looks like a little bean & sac is still visible.

Yes: Better at 8 weeks is to have a vaginal ultrasound as they are much more accurate for dating pregnancies this early. A vaginal ultrasound should be off by at most, +/- 5 days, no more. Definitely not a month. Ultrasound is possibly more accurate at this age than is last menstrual period. If LMP and ultrasound differ by more than 5 days, doctors will use ultrasound to date pregnancy.