This is what I use to display a map with 3 pins/markers:
I've tryied all answers of this topic, but just this below worked fine on my project.
Angular 7 and AGM Core 1.0.0-beta.7
The properties [agmFitBounds]="true" at agm-marker and [fitBounds]="true" at agm-map does the job
[agmFitBounds]="true"
agm-marker
[fitBounds]="true"
agm-map