New Terran player question on loading medivacs. Hi guys,

I'm new to terran and I'm having trouble loading units into medivacs. Let's say I have a couple medivacs and I select my army to load up as many units as I can into my medivacs to send them out for a drop. Once I load as many units as I can the rest of the army keeps following the medivacs as I send them out.

Is there an easier way to load and prevent the left over units from following the medivacs?

Thanks!