Please pay no attention to all the "you're only 16" crap. Just do it. Scandinavia is very safe, especially if you're blond. check if the driver isn't drunk, which is a pretty rare occurrence there, since alcohol is EXPENSIVEexpensive.
There is a law in Norway the Outdoor Recreation Act of 1957, where you can pitch a tent on a field, for two days for free. http://www.switchbacktravel.com/norway/public-access
I guess this works in Sweden https://naturetravels.wordpress.com/2008/02/08/wild-camping-in-sweden-and-the-right-of-public-access/ and Denmark too.
However....If you're white, and claim you're from Western Europe, you're save from racists, and Norway has plenty of those. I wouldn't recommend this if you are a visible minority, you could be harassed, beaten up or worse.
your biggest problem is then your stay in Poland and getting to Scandinavia.