Well done for having the balls to try some thing
I assume you must have used 2pack with how that's come out ?
Why not sand it down and try it again?? I would thats how you learn
You need heat with the cold weather and it will help the paint flow.
Regarding your line, you need to get a soft edge, best way it too paint up the 1/4, cove it but leave a gap i.e not tape it, once youve painted, you spray a small amount of fade out thinners to it too keep the edge very soft and then when you flat and polish you get the line gone and you cant see were you painted
I personally prefer Paint Shop Supplies!!