You are not wrong - this is a large species! Macrolepiota dolichaula is frequently up to 17cm. distinctive because of the size of it; tends to grow in grass; tall narrow hollow stipe (stem) slightly swollen at the base; moveable annulus (ring) high on the stipe; uniformily white colour, sometimes very slight hint of colour in central umble; immature fungi look like drum sticks; lamellae (gills) free. Good photos capturing diagnostic features.