That's the standard width for the gates. I don't think you can change them. The exit gate is wide enough to line up with a 4m path, but the entrance gate for some reason is designed for a 3m wide queue. I just use a 4m queue and let it taper inwards when attaching to the gate.
You can sort of freely move gates anywhere along the length of the platform, but they are designed to snap to the middle of 4m grid squares. You can put them elsewhere but as you get close to that middle point it snaps to help you get it aligned. And generally speaking that's a good thing, that's where you want them so they'll work with whatever station building you're constructing.
You're probably having problems attaching a path and queue because of interference with a wall or floor you've built. Save your game and try deleting building parts in that area, attach the path and queue, then rebuild around them.
BTW, do you know about the "build on station grid" button? It's easy to miss. When you select a station platform of your ride, there's a small button at the bottom of the properties window which lets you start building on a grid which is aligned with the platform itself. Essential for getting things to line up.
Hope this helps!
