as polyester resin ages it gets thicker until it reaches a no use stage. until it becomes a thick gel, it is usable. Heat, as in a hot garage , makes it age faster. Actually, that is the purpose of the accelerator, to generate heat so that it hardens quickly. If you notice, when you mix the resin and accelerator in a cup, it gets hot, If too much accelerator is used, it can actually cause a fire.
To slow down the process, you would chill the resin before adding the accelerator
By now the mix you made is probably set up, your ratio is about O.K.
As an aside, if the mix doesn't harden, you can warm it with a hair drier. You can actually get it to set up without an accelerator, just by keeping it warm