Imhotep has been sentenced to "the Nameless Death," yet his name is still inscribed on his coffin. The ancient Egyptians had chisels and should have been able to destroy the glyphs on the coffin that make up Imhotep's name, but it is untouched when his mummy is found.
In the flashback scenes of Imhotep being mummified, his legs are bandaged together. They are still bound together in long shots of the mummy in his sarcophagus (which was a dummy). But when he comes to life, his legs are bandaged separately, allowing him to walk.
It is said a few times in the movie that princess Ankh-es-en-amon was a vestal virgin. Vestal virgins were in fact part of the Roman religion (they were priestesses of the goddess Vesta, hence their name), and had nothing to do with ancient Egyptian religion.