Need help with modelling a Juice Spout Pouch Blender noob here! Just started learning how to use blender a week ago and I am having troubles creating a mesh of a juice spout pouch with the left, top and right sides sealed, I did one using a plane and mirroring and extruding the edges, but the mesh is a mess and I cant create the bottom of the pouch so it is just a hole.
What I have:



The edges are actually a big mess because I used a plane and mirror, then extrude it, so there's some volume, but the sides are supposed to be sealed together and thus have no discernable volume (I hope this makes sense). It looks somewhat fine from top down camera angle but I want to know how to actually model this correctly :/ I also attached 2 images of meshes that I am trying to achieve! It's from a model on cgtrader, I can't figure out how to achieve that. Thank you so much for the help! *TLDR: Is there a better way to model this than plane &gt; mirror &gt; extrude edges? Can't seem to get that bulgy rectangle in the middle with flat, sealed edges at the sides.
What I want:
You can select the bottom edge loop by going in Edit Mode with  Tab, and choose the edge select mode.
Then select an edge from the bottom while holding down the Alt key, and press  F to fill your bottom.