Those measurements per foundation? If so, maybe the should be a bit bigger, like 78 x 78 x 38, I think then it would be easier to fit stuff in.
But there are 49 foundation spaces to be built on, even if they are 64x64 that is a lot of space. You aren't confined to just one 64x64 plot, thats just for planning and measuring purposes, you can build wherever you want, as long as you don't claim an unreasonable amount for no good reason and as long as you are on the correct tier (no building blocks of flats in corporate district for example).