Welcome to HCM.
You were carrying early wk pregnancy
. Early HCG test may be negative as some kits not able to detect low level hcg. Later on 23/6 you got positive HCG test and USG scan revealed early intra uterine pregnancy.
Actually gestational sac
first appear around 4wks on USG scan and measurement is 3-6mm. You got gestational sac size of 0.5 cm that means your gestational age
On 21/7 your gestational age will be 8wks and you will get CRL 16-20mm,length 0.6-0.9 inch,FHR around 160 with prominent fetal pole
Be well and happy journey of your pregnancy.