Even if you lose focus it's ok don't judge yourself saying like: " I should be more concentrated or stuff like that".
Meditation (at least for me) it's all about accepting yourself and your thoughts.
I raccomend you trying the app calm or simple habit instead or the details meditation here.
That being said some days are harder than others. If you are tired, hungry, stressed it will be harder but you just have to push through.
I am working nights so I don't have the energy for long meditation in the morning so I have been doing under 10 minutes most days.
The closest I’ve come to that when not on retreat is when I’ve been maintaining a daily practice for a while. But it’s still more of a struggle because the stress of daily life pulls my attention away from being present.
I think if I was sitting longer daily, say half an hour or more, then it might get easier over time. Unfortunately, I don’t have that kind of time given all of my responsibilities.