Foolish Sauron...

[The Might]

I don't think he could make such rings by himself. Think about it, if he had the possibility to make such things then he could have created hundreds, thousands even. But he needed the smiths of Eregion to make them for him.

Indeed he made the One, but the One is totally different from the others, it is the Ring that controls all the others.
And when he told the Elves to make them he probably thought that this quantity would be enough for him to enslave all the free people of M-e.

For in that time he was not yet evil to behold, and they received his aid and grew mighty in craft, whereas he learned all their secrets, and betrayed them, and forged secretly in the Mountain of Fire the One Ring to be their master.

So clearly he did learn some things from the Elves of Eregion.

Or maybe he simply was not able to control more with the One Ring...although I don't think this is stated anywhere.