Applied to thickly at a guess for starters.
No problem doing the whole car and leaving it, I find this the best way when using EGP and it is what Autoglym recommend. I always leave it on for an 45 mins to an hour at least, comes of super easy when applied thinly. I have left it on over night before in the garage and then removed and it wiped of even easier. Apply it so thinnly you can hardly see it, when you think the coat is thin enough it is probably still to thick! Anything you wipe of is just wasted product.
Not one to use in the sun though or it will bake on!