ok. so let me make sure I understand, you have the domain, dryrunbaptist.org, but there is no email defined within the domain settings in the DH panel, correct? I would assume not as I see your MX records all point to your googlemail server. I would assume that has been setup to send/receive email for that domain as well, and is working. The 2nd thing is that when I did a lookup on the DNS name of webmail.dryrunbaptist.org, it doesn't resolve. So that sounds like you need to add the record to your DNS settings. So, if this sound correct, here's what you need to do.
Panel -> Domains -> Manage Domains -> DNS(for the domain dryrunbaptist.org)
Here you should put the following.
Value: Googles webmail page, or whatever page you what that URL(webmail.dryrunbaptist.org) to point to.
Comment: Whatever you want for reference.
I believe that should accomplish what your trying to do. BTW, for your reference, what your trying to do is add a 'HOST' record, not a subdomain.