Well - it usually hard to get newly hatched shark pups to eat. Most people who are very experienced then to lose at least half of newly hatched sharks.
For this reason - it generally recommended that people new to keeping sharks or rays start with young sharks that have been feeding for several months. These sharks usually adapt to feeding more easily - because they already know how to do it. Plus hatching - is a very stressful process for shark pups.
So don't give up yet - just attempt next time to get one that's a few months old on it already - you'll likely have more success.
For most species of "home aquaria friendly" sharks -i.e. bamboos, eppis, coral cats, or horns - that is about 8-12". These tend be a little more expensive but are worth it.