18 high BT with negative pregnancy test

This is my first month chatting and our first month my husband and I are TTC.  
I believe I ovulated on day 13, due to cervical fluid and a spike in temperature. 
However, Fertility Friend thinks I ovulated on Day 23. 
Assuming that I ovulated on day 13, is it possible that the pregnancy test I took last night was too early? We were excited about 18 high temps and puzzles when the test was negative. 
Thanks for any help!