HELP!!

First sonogram measured me 8 weeks and 5 days but GA says 11 weeks and 5 days on Sept 7..I have a due date of 4/14 with the measurement of 8 weeks and 5 days but with GA of 11 weeks and 5 days the due date is 3/25 basically giving me the lmp of 6/16...Which is 3 weeks apart..I am currently 28/29 weeks..Ive had a period of 7/15 which should give me the due date of 4/21 which is only 7 days off from LMP...What does that means?? When is my correct due date and when did I conceive??