Cover line vs Luteal line???

Josie

Hi ladies! I am looking for some help. This is my first month temping, 4th month TTC. I’m confused by the difference between cover line vs luteal line on my chart. Also, does temp gradually or suddenly drop before period? Last 3 days steady drop. AF is due tonight/tomorrow. Am I out? 😔🤞🏼

Appreciate any help!!! 💕