Pencil holly branches are bowing
Branches are falling to a horizontal position and will not remain vertical.
From this picture it would appear they have grown pretty wide.
They need to be pruned in order to gain stability.
Prune back any branches leaning out or crossing over.
Prune them all the way back to within an inch or so of the main branch.
Prune the top and sides every 2 to 3 months during the growing season while the plant is young. This will force the plant to build stronger stems below and as the plant gets taller and larger it will be able to support itself.
Only use a slow release fertilizer, this will make sure the shrub doesn't grow to quickly from a quick shot of nitrogen.