curious..earliest a scan will show pregnancy is where it should be

Elizabeth • 3 ectopics(2003,2010, 5/2018) 1 m/c (3/2017) no babies :( 35 still trying

when you have had an ectopic the fear is always there so I'm wondering what is the earliest a scan will show if the pregnancy is where it should be? we thought mine was where it should be but it was just a sac & the baby was growing in the tube.