Connecting to AWS RDS SQL Server from Appsmith

Hi there. I just created an AWS account and an RDS SQL Server database intended for some quick "proof of concept" work but I can't seem to successfully connect to it from Appsmith. I simply created the database with "default" settings aside from going back and making sure that it was publicly accessible - should that not be enough to be able to connect to it from outside, using the endpoint as my host address, port specified as 1433 and the username and password that I assigned? I'm getting the "server was not found or was not accessible" message. I did find that I had to add an inbound rule for my default security group for MSSQL of CIDR block 0.0.0.0/0 in order to successfully connect via SSMS, so I tried similarly adding inbound rules with CIDR blocks equal to the IP's that Appsmith uses but I'm still unable to connect from there.

I'm a real newbie to setting up an AWS environment, so apologies there... again, I was just hoping to use if for a quick proof of concept but my inability to connect is throwing a wrench in that idea.

Thanks.