Where was silicone used on the gasket?
The Magnum gaskets do not usually leak from the sides, unless like others said the pan bolts are bottoming out or like you said something is wrong with the pan. Usually they leak from the front in the corners when used with an LA pan and that runs down the pan rail.
The corners are the only area that should get silicone and I always fully tighten right away since it is filling a gap. Here is another thread with pictures of the Magnum gasket and LA pan differences.
Magnum Oil pan/gasket fitment issues