When to have my early scan

Katie • 27 years old, married
Hi all, my scan appt is for a weekend so the above are my options. It's typically called the 7-8 week scan to check for a heartbeat, date the baby and check growth.  
I am in two mind when to book the scan as I want to know ASAP if baby is developing ok but also thinking if I hang on another week or so I will see more and we can use the scan to announce to our parents when we are a bit further along. 
When do you think I should go? Any reasons welcome in comments 

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