There's a few things going on that will make this feel less stable.
First, and I'm not 100% sure about this, so possibly ignore, but it looks like in copying the design, you've stretched the main deck wider than 30" and shrunk the diameter of the feet fractionally. This won't be a huge deal, but everything counts.
Second, the deck looks like 1/2" OSB, and the combination of 1x2, 1x3, and 1x4 (we'll call all that the "subframe", for lack of a better term) probably isn't sufficient to make that into a stiff surface. It can help to drive a bunch of 1-1/4" screws from the top side through the subframe. The 1x4 that turns into a 1x3 on the right side of the picture isn't helping as much as it should -- a continuous piece of wood would be much better. To stiffen this surface, add more wood, with screws from the top side of the OSB. To really stiffen this surface, make a torsion box with another layer of OSB on the bottom.
Third, and the biggest issue, is that you've stacked flimsy 1x2 rails on top of different subframe members. It's not clear how these are attached (except for a couple of visible t-nuts), but you need to pack the empty space between the legs and the top with solid wood. That means a 1x6 (or bigger, if it'll fit) between the main subframe and the two 1x2 rails, and 3 strips (as wide as possible) between the subframe and the feet. The end goal is that the tops of the feet have wood between them and the OSB top. Now attach from the top side of the OSB through the padding, into the tops of the feet with plenty of 3" screws. Predrill clearance holes in the OSB and the 2 layers of packing, and pilot holes in the foot.
Parenthetically, it's not clear to me why you opted to add those 1x2 rails that run sideways. If they're needed for stiffness along the 6' axis, put them out at the edges. (Better yet, put them on edge around 4 sides like a table apron, as opposed to on the flat.) As they're placed, they're not really helping and will cause upholstery trouble later on.