17 week or 22 week scan???

Beatrice
So my doctor recommended that i get either an Initial anatomy scan between 16-18 weeks OR a detailed anatomy scan between 20-20 weeks. Because of scheduling I wouldn't be able to get my 20 week scan until the end of the 22nd week. 
I am eager to find out the gender - and am thinking i'll just go to the 17 week scan and skip out on the 22 week scan (extra money!) 
What are big differences between the 2? They said they'd be able to tell me the gender but is there anything else im missing out on by not going to my 22 week scan?