Hi there,
Welcome to OPM! There are plenty of folks here who also post regularly on SDN. It is out sister site.
There is no set number of volunteer hours that you must have to apply to medical school. You should have at least a physician shadowing experience in addition to your volunteer work but your previous hospital experience should be enough.
I do not see where you need to update your application as long as you have some volunteer experience that indicates an interest in your fellow humans. This can be hospital-related but it can also be working with the homeless or working with abused children etc.
Natalie 
Welcome! I think you have done great! Hang in there!
By no means are you outta the park on this, I think you need to spend some time on creating a package about you for your application. Things that when a person reads about you they get excited about you wanting to be a Doc! Volunteering, any is fine and your enthusiasm about volunteering should come out in your statements. I would spend a good amount of time writting and reading and rewritting it, have other’s read it, see if you can have some people read it that are your friends-friends. I do not think ADCOMS are the way you have been told.
Anyway thats my 2 pence
good luck 
I also think that you have enough clinical experience from you one year gig plus you what you are doing now…have no clue why that adcom expected more? it is NOT about amount of hours but just enough exposure (although to be quite honest nothing prepares you for the reality) to make sure that you “know” what you are getting into…seems like you are doing a fine job btw.
thanks everybody for your wise words and encouragement! it definitely helps. it’s hard when you don’t have any other friends going through similar experiences. some of my doctor friends who are doing their fellowship or are attendings now don’t even understand, i guess they went to med school when the competitive climate was different. they are like “what? you have to volunteer and do all that to get into med school?” geez.
anyways. i am in the er at the new hospital, and it’s very good. i think if i log in enough hours i may even get a doctor to shadow . i will send that update letter in the new year so the adcoms can see it when they get back from the holiday celebrations, and hope for the best!