ClearBlue fertility monitor

Evening ladies,

Has or is anyone using a clearblue fertility monitor?

I started this weekend and had 10 sticks to use but unfortunately 2 were wasted due to faulty readings. I only have 5 left of my batch when I need 7. I red it says to stick with the same batch number of fertility sticks.

I'm now worried I haven't enough and may miss peak? Or shall I just buy another lot and use?

Confused can anyone help? Thank you!