hey, sorry I have only just seen this thread, I really hope the info I'm about to give you will help you to relax a little.
I'm currently 19w+1 with pregnancy number 4, I have had a previous mmc, ectopic and mc so it was recommended for me to go for an early pregnancy scan at my local epu at 6w.
LMP 29/11/11
BFP 31/12/11 (4w+4 from LMP)
Scan 12/1/12 (6w+2 fromLMP) - no signs of baby!
Scan 26/1/12 (8w+2 from LMP) - follow up scan, baby showing 6w+5
Scan 30/1/12 (8w+6 from LMP) - bleeding, baby showing 8w+2
Scan 1/3/12 (13+2 from LMP) - 12week scan, baby showing 12+4
Every baby grows at different speeds, I should have been 8w+2 from my LMP before baby was even visable on scan, i was convinced i was going to have another ectopic pregnancy, but luckily this was not the case. I really hope everything works out for you like it has for me and my DH this time.
It can be too early to scan, internally or externally, so dont worry yet! you are getting + HPT's so dont panic!
Really hope this helps a little?