Do you need to make them that large?
If you narrow the finished size of the top to 60 inches or narrower, than you could (depending on the design of the backing) get by with one and a half widths of fabric. Which still comes out to about three yards of fabric. (68 + 34 = 102 inches -> okay, it's 2-5/6 yards. This does not give you any fabric left over for borders or wiggle room.
If you went to a finished size of approximately 40 inches wide by 60 inches long - you could squeak by with one width of fabric.
Many fabrics are only 42 -43 inches wide - even before washing - so one and a half widths of fabric would not be wide enough for a 64 inch top anyway - after accounting for selvages and seams
I came up with a need for approximately 3-3/4 yards of fabric - assuming two inches "extra" around each side of the top - and this does not take into account any possible lengthwise shrinkage of the fabric if it's washed before cutting or if it's cut crooked and needs to be straightened out.