I honestly think those stone patterns in sims 3 are terrible they seem to repeat soooo much. Is there a way to make the picture of one square bigger so it seems less repetitive.

Nope. Pattern tiles can only be 256x256 pixels in size. I suppose, however, that if you wanted to do bigger stone patterns for exterior walls for instance, you could do what people did in the Sims 2: make a set with two, three, or four patterns that match at the edges, and get people to alternate them when patterning a wall or floor.

You'd still get the vertical tiling on walls, but again, it would be possible to choose a wall object with two or more patterns in it arranged vertically, and construct two or more patterns designed to tile at the edges of the different pattern regions. This part would be quite tricky with the included wall objects, since the pattern regions don't necessarily correspond to pattern tile edges. Of course, you could also modify the existing wall objects or make a new one that would map patterns the way you want.

So, yes... that would solve your problem. Would be a fair amount of work, but it could certainly be done. Haven't seen any pattern sets set up like this yet, but you could be the first!