8 weeks...to tell or not to tell?

mjbaby

So I calculate that I'm only 6/7 weeks pregnant. My OB calculates I'm more like 8/9. I'm not sure why my OB seems so different than everyone else's on this board, but she doesn't even want to see me until 9/10 (appt 8/23) weeks! WTF? I know I'm pregnant, but I have no idea if it's viable or if something is wrong, etc...
Back to my problem. I'm going shopping with several pretty close girl friends from work on Monday. None of them know I'm pregnant, but we are going to an outlet (that I almost NEVER go to on my own) where there is a maternity store. I KNOW I will be so tempted to buy discounted clothes, but obviously I don't want to do that if I don't tell the girls. So - 1 - should I tell them? These are friends that I'd tell if I had a MS, so that part I'm less nervous about. 2 - Should I buy any maternity clothes yet? Is it a bit presumptuous to start buying maternity wear when I haven't even seen the Dr? Advice, wise sages?