Octave and Tuner

I'm assuming the "I Have Seen Where I'm Going" song in sung with notes around "Middle C" on a piano.  And as I understand, that Middle C is referred to as "C3."  The C above it is C4.  The C below it is C2.  I have great difficulty discerning whether the notes I'm singing are the same notes that are being sung in the lesson.  I'm not sure if I'm singing in the right octave.  I can sing quite a few songs well, but this practice song seems out of my range.  I believe I must be singing notes that are either harmonizing with your notes and/or an octave off.  Because the song in the lesson is sung along with piano chords, it makes it difficult to pin-point notes even using a tuner.  I have a chromatic tuner.  I'm not sure what setting (instrument) to use for my vocals.  And I don't know how to determine the exact notes of the practice song.

Middle C is C4, so you may be more confortable starting at C3 instead! Please feel free to sing in whatever octave is most comfortable for you. 

I use tuner.ninja or an app like Vocal Pitch Monitor!

Thank you so very much for all of that information.  Extremely helpful.  :)

Since the instructor plays chords along with his singing, is there a way to find out the notes of the melody itself to this practice song?  I've tried deciphering them using an online piano, but don't seem to be able to do so.  So, what I am wanting is to make sure I'm singing the same notes the instructor is.  When I try to use a tuner with his performance, the tuner is picking up the chords and his vocals, I believe.

I will ask to see if there's a lead sheet available! Which instructor & course is the song from?

Thank you.  It is the beginner course by Jonathan Estabrooks.

Thank you, will update when I hear back!