Inserting Sail Ribs

They are battens, not ribs. They won't be flush, as shown, the strap , belt like goes around the end then into the buckle, you then clinch it up. It then pushes in and makes a foil.
Do you have more battens, than pockets ?

the one pictured looks about right for length.
This sail is rather old, while the adjustments all matter, don't fuss if it's not perfect.
You need to : after the battens are installed, tightness not important at this point, apply downhaul, pull the sail down to shape the foil, outhaul which is the clew end of the sail, out to the boom end. Both these numeric should be printed on the sail , bag, or both, a guide. I would tighten the battens after downhaul, before outhaul.
the precise settings , are approximate, a starting point, depending on many factors. This sail due its age is not so critical.

ive mentioned age, that doesn't mean it won't be useable, the board is important also.

The flexy end of the batten goes next to the mast, in your pic It looks like you've laid the batten on the sail backwards
there should also be a cap on the end for the webbing strap to go through

Are you in Australia? I have lots of these batons and some end fittings too if you need them, a great trick is to wrap them in heat shrink as they were prone to fibres pealing off and slicing your hands or worse splitting in the sail and slicing the fabric. From memory the Neil Pryde Wave sails had the grey batons above the boom and yellow tapered ones below the boom. I still have one old NP Wave from back then a 3.3M but you may find like mine that the fabric is letting go and breaking down, they are pretty old now.
Cheers Pete.

Email sent you. Me, I did, just now.