Widget sizing/appearance was probably the only surprise that I discovered between Nova and Octo. Resizing in Octo takes a bit of getting used to, but I was able to reproduce the appearance of all of my widgets.
Padding is a little different and harder to discover than Nova - it is in the "Customize appearance" menu when you long tap on a widget. That is something to check out, as well as making sure Rounded Corners aren't enabled.
There is also a "Freely position and resize items" option in the Launcher Settings->Home tab, which I do not have enabled, but might be necessary to get your widget sizing just right?