Try fretting the chord without the pinkie to get a good anchor- or even make sure you've got the 5th down with two fingers first, and then move on.

The key idea is to make sure that your hand gets stretched and strengthened enough to reliably hold these chords.

If you're having trouble with one chord, move on to the next one. The exercise will give your hands the ability to form these patterns. If you keep at it, you'll notice that you're getting better every day!