Yes, it's only the first pin. You can split the loading dose into two also if you wish. The "loading" dose for 500mg is 350mg, so you could split 175mg+normal injection so on monday you inject 250+175 425mg and then thursday again 425mg. Does that make sense? Because you are taking the number which is being loaded "extra" and dividing that into two. I prefer doing it all in the first injection but for sustanon, for example, splitting the load up in two makes more sense.
500mg Test E/week frontload would be 600mg on the first day, after that do your regular injection schedule.
600mg Test E/week frontload would be 728mg on the first day(round up or down to nearest most convenient measurement 750mg is fine)