You have missed a point about sacred sunrize: Sacred sunrize dont do any damage untill you use a holy spell. When you cast sacred sunrize you apply a debuff on the target and this has a timer that counts down for some seconds. You are supposed to use a holy spell either righteous word or interdiction before the timer runs out. If you wait untill the timer have run out, then you have wasted the sacred sunrize.
You need to understand also, that loosing agro is always a possibility. If you party up with someone who deals huge amount of damage compared to your agro, then you will loose agro. Also some mobs and bosses are random agro. So loosing agro is not necesarily because you play badly.
Loosing agro is not always a bad thing, especially not in fights against normal mobs or elite mobs, since most other partymembers can take some hits without dying. Loosing agro in bossfights can be fatal. Loosing agro to the most squishy partymember is most often a bad thing, but that is not only your responsibility.
I suggest that you use the rotations recommended in the classguides for paladin. IMO Efinkas [PMB] guide is the best of the guides.
I also suggest, that you make an agreement with your party, that they wait a few secs before attacking, especially if they die easily - so that you have a little time extra for getting agro.
On a side note, your thread should have been in the paladin subsection.