anal gape tips

hi, m17, lately i've bene trying using an anal dildo (1.5 inches width), i use It almost as a plug keeping It inside for hours. One of my fantasys is to achieve an anal gape, but i noticed that my dildo isnt enough to give me One, so i tried a 2 inch width bottle, but i struggle to keep It for more than a couple of minutes, and It Is also not enough to get me a gape. So how can i progress in order to achieve One? Is there something in particular that i should try? Whats the minimum size that could get me a gape?

Sorry for the english and thank u