Did you actually measure the temperature in your attic and more importantly the temperature of the epoxy and the fabric? If not, it's really hard to determine how thick the mixed might have been.
Viscosity (thickness or stickiness) increases as the temperature decreases for virtually all materials, and furthermore in mixed epoxies, the viscosity increase with time as the resin reacts with the hardener(aka linker). Thicker resins are harder to mix, and will take longer to mix completely at lower temperatures, and colder resins will take much longer to cure.
The viscosity of your resin PR2032 is listed as 1650 cps @ 77 F (25 C). The viscosity of your hardener PH3663 is listed as 35 cps @ 77 F. The initial mixed viscosity is listed as 440 cps @ 77 F. If the temperature of your materials were actually 59 F (15 C) then your mixed viscosity could be as much as 2.6 times thicker or ~1150 cps which is higher than the viscosities of PR2032 with PH3630, PH3660 or PH3665 when mixed @ 77 F. Using a thicker mixture would make it more difficult to wet out a fabric and the mixed resin would feel sticker than a warmer mixture.
Your experience illustrates why it is so important to follow the manufacturer's instructions when you use professional epoxies. You simply will not get the results you expect to obtain if you don't. You can to try to save your composite by heat curing it. Make or find a box that is longer than the item and several inches wider and taller than your piece and flow warm air through the box. If you have hot air heat, place the box with the composite in front of the hot air register and allow the air to flow through the box for a day or so. If you have hot water heat, place the box on top of the radiator for a day or so. This should cure the resin. If the resin was not completely mixed with the hardener, there isn't anything to do but do it over.
Good luck.
Bob