Are we being scammed?

Sorry, but this was an impossible situation from the beginning. The owner of that OpenSpaces sim was offering something he could never deliver. Changing the Object bonus does not change the total prims available in the sim.

There was, briefly, a known bug that allowed a sim owner to set an OpenSpaces sim's prim allocation bonus higher than 1.0, and you actually could put that many prims in the sim. BUT! This was known to be a bug, and one that LL was certain to fix in a future server update. Any sim owner that had done the least bit of research about how sims work would have known that. And would have known it was a situation that would not last.

Making sure you had to re-sell some of the parcels in the sim forces you into a position of being the "bad guy" when those parcels are all sold, and the residents find out they can't use their promised full allocation of prims. It also made it likely that you would not realize right away that there was a problem, until several of the parcels were occupied.

Furthermore, though that sim owner may have sold you all 4 parcels in that OpenSpaces sim, they COULD NOT sell you the whole sim, unless you already owned at least one full sim of your own. So it was deceitful to say they were "selling you" the sim. They were only selling you 4 parcels in that sim, but they still own it.

When your paid-for time is up, leave, and do no further business with that individual. It is unlikely they will refund your purchase price, and you can not honorably sell your parcels under similar conditions to others. Walk away.

At best, they are an incompetent sim owner. At worst, a deliberately deceitful one.

These days, more and more sim owners are moving to a business model of taking no deposit up front on leased parcels, and asking only for a monthly maintenance fee to cover tier. Shop around. You can quite probably find a sim owner who will rent you a full OpenSpaces sim, or a parcel in one, for little to nothing down, and a reasonable monthly rent.

It is unlikely the Lindens will do anything about it, but I would still abuse report the sim owner for their deceitful business practices.