According to the FAQ on the Accuquilt website, when the blades are at an angle you need to angle your fabric -- so the fabric is supposed to be lined up with the die blades.
Selvedges would be along the side of the die (not at the top).
Coffee filters from the Dollar Store on top of your fabric are a cheap way to use paper to stabilize the cut.
Starching the fabric before cutting will help too.