I took a few more pictures. I think it should work, but I noticed a couple of things. Looking back at your picture where you show the parts, it does look like the front bracket is bent at the end with the bolts. The bolt end should be flat, not curved up where the bolts are.
The back bracket I think you have bolted on correctly. This one is kind of blurry, but I believe it compares to where you mounted yours.
The front bracket bolts on the bottom lip of the deck, the second and third holes in, but it should be flat under there - yours looks like it is bent. Perhaps you can mount it, then crank it down (unbend) so it sticks out straight. For now, ignore that orange metal baffle insert in the deck. That bolts on totally separate and doesn't come into play at all in putting the boot on.
Note that first hole isn't used, next two holes are for the bracket, other holes for the baffle thing.
Here the boot is just off the brackets. Notice how that front bracket sticks way forward, parallel plane to the deck - I think if you bolt yours on it will curve back toward the deck. But if you go ahead and bolt it on (it goes under the mower lip, bolts through the lip) I think you can just step on it or something to bend it down flat.
And then attached with the pin in the back and pin in the front. The front of the boot fits into that space between the deck and bracket sticking out there and slide the pin down through.
On your original picture of the parts, I didn't see the orange metal baffle thing. This bolts onto the deck, again in existing holes, and narrows the opening of the shoot so that the clippings go into the rear part of the boot. Without that, I think you are just filling up that front section but most must be exiting through the back open section and on through the tube. I think you should have that baffle though, as it will direct the clippings better the direction they should go. It will probably give you better suction from the PTO fan on the back as well - I'm sure it's all engineered for that. It may not clog as easily...