Early scan- low rise hcg but seen baby and heart beat

Had an early scan thinking I was 6w 1d. We were worried about an ectopic due to low hcg and rise not quite doubling with some Betas.

Also had 4 days of spotting before BFP and then another lot of 4 days of spotting during 4-5 weeks

Scan showed baby and heart beat 5w 4d and a heart beat of 110. I was very surprised because I really expected to see nothing and to miscarry after hearing my numbers.

9/3 138 4w 1d but actually 3w 4d

22/3 179 4w 4d but actually 4w

26/3 980 5w 1d but actually 4w 4d

30/3 2600 5w 5d but actually 5w 1d

2/3 had another Beta done today

So confused with how it can be off because I tested positive so early. I’m in shock