Using Route53 registered domain with Shopify online store

Question

I bought a domain from AWS through Route53. I am trying to link my shopify store with this domain. I tried the following configs from shopify,

1. Added a new CNAME record with name = www.mydomain.com, and value = shops.myshopify.com.
2. Added a new Alias A record to route 53 with @ name and value = MyStoreIPAddress.

When I verify my configs over on Shopify, I see this error,

I tried following this post but I am not really sure where should I copy the NS records values? Since I bought the domain from route53, I am assuming that correct values already exist for DoNS settings. I also noticed that route53 propagation happens really fast so I dont need to wait for 48 hours to see the propagation results. My store still isnt linked properly. Can anyone please provide some pointers? Thank you!