Am I damaging my vocal cords?

Question:

Am I damaging my vocal cords?

I had my first singing lesson last week Saturday and all we did was talk and place my voice. She said I had an exactly one octave range starting at low C to Middle C. I wanted to expand my range (The notes I couldn't get were in my passaggio, my passagio cover about one hole octave). So for the past two days I have been practing for about 20 mins. trying to go up higher little by little. I tried and it seemed impossible to sing a D. But now it is gradually getting easier to go higher and higher. When I practice going higher my vocal cords do feel a little stressed for about 15 mins. after. Am I damaging my voice or is this just stress from stretching.

Additional Details

8 months ago
when I say practicing I mean just trying to slowly go higher or lower. We only had one lesson and she hasn't taught me anything yet.

Best Answer - Chosen by Asker: 8 months ago
when I say practicing I mean just trying to slowly go higher or lower. We only had one lesson and she hasn't taught me anything yet.