Before you "rack the shot gun", you need to work on this "I'm actually a little nervous about the response being overwhelming" If you don't reframe that subconsciously you won't give you marketing efforts 100% and it will hold you back.

Also, you client isn't the medical clinic, you have two clients the decision maker for the clinics who approve the purchase and the users of the app who will help convince the decision maker of the benefit. For the decision makers, I'm thinking trade journals off and online, If employees would be using the app they or the decision makers gate keeper may be on LinkedIn or other industry specific platforms.