he didnt do anything wrong, you got shitty springs, granted that thickness hass ALOT to do with it, the thick ones are shorter because of the weight difference of the back to the front with the engine, the front ones are longer and smaller for a better response and the length to compensate for the strut length and the weight of the engine! he put them on corect, ya just got bad struts or the springs are bad....call skunk and double check but the thick ones do go in the back, thats why they are shorter, you put those short springs on the front and youll kiss the ground