Here are some pix of the bottom. My fingers are pointing to the diagonal braces.

You did a 5 stringer wide bridge, and mine is a 6 stringer wide bridge, so you will need to resize those parts.

Also, the curb should hook under the transom beams like this. My tweezers are pointing to the locking tabs on the curbs being hooked under the transom beams. This should capture the wood pieces.