I am also using RCM ear training web course on a Mac with external microphone. The recorded volume within the online course is still somewhat lower than expected, but loud enough for its purpose.
Just tried the course on iPad this morning, and I get the same problem of recorded volume so low. BTW iPad's own Voice Memo App records just fine with adequate volume. So this is problem must be specific to the RCM course as it uses Safari to access the built-in microphone and record. iPad's built-in microphone does not allow gain adjustment. So I agree that the solution is to get an external mic - specifically one that has built-in gain control (a.k.a. volume knob). Of course you could also get a regular mic and an audio interface, but the complexity defeats the benefit of using an iPad.