Setting up inbound-rules for Security Group when creating an RDS instance

I'm trying to connect to an already-created Postgresql DB Instance on AWS' RDS but am not succeeding. Here are the steps that I took:

• Created a Security group from the VPC Dashboard. I wasn't sure how to set the inbound rules (didn't see any details about this on AWS docs). Currently I just put it like this: inbound rules

• Created a RDS instance with the Security group created in the previous step selected.

• After the RDS instance's status says "available", I run the following command to test if I could access it:

nc -vz myinstanceendpoint.cmasxwfasdvanxaw6pwc.us-west-1.rds.amazonaws.com 5432

• I'm getting the following error:

nc: connect to myinstanceendpoint.cmasxwfasdvanxaw6pwc.us-west-1.rds.amazonaws.com port 5432 (tcp) failed: Connection refused

Any suggestions would be appreciated. Thanks!