what should I expect

On Friday I have my first class ultrasound. By my reckoning I should be 8 weeks and a few days, the mid wife says it could be up to 12 weeks and a few days (I don't think so as wasn't pregnant on 10th august, took provera on 12th fur a week then in 24th got positive test hence I don't think 12 and I'm SURE it's 8 weeks and a few days) so I'm wondering what exactly will we see on the scan if I am 8 weeks? Will we see head/heart beat??? Or just a sac?? Any ideas would be great