Surely you mean four sheets: 3x 4'x8' for sides and top, a fourth sheet cut in half for a 4x4 piece in each end?
Without a stronger shape, you may get blown over.
(This could be solved with some external 2x3, 2x2 or 1x2 supports (external triangle buttress, however easiest for you to make), if you want to go that way. Each triangle to be staked to ground. Minimum one in the middle each side. A pair on each end too? Extra transport weight of the wood, but the wood is reusable next year and it does keep the tape length down.)
With only four feet across, you may get heat-creep through the sun-heated ground outside, so it may not be as cool as larger yurts (total footprint may not have enough ground cooling to counter the sunny-sides' heat-creep). You could counter this with something on the ground for a few feet on the sunny-sides to reflect the sun away, but expense and hassle to make sure it won't take off in the wind, or what ever is holding it down doesn't trip people up.
Here's someone doing a three sheet A-frame.viewtopic.php?f=277&t=56116
Odd. No bears to watch in the dump. Oh well, lets go across the road & pick blueberries.
... but don't harm the red dragon that frequents the area from time to time. He and I have an agreement.