too wet of a concrete mix and it will find its own true level when tamping it
you need a lesser wet mix to be able to tamp it but also for the stuff to hold the form that you are wanting to hold you wont get the sheen on the concrete but you can float it well enough though
at 10º out of concrete by what distance ? or is that the full length required slope to be raised
how thick is it at the thin end? - if it's sloping down to nothing you really need to dig down at the thin end to make it a bit thicker or it'll crack straight away
you don't need a frame around it depending on setup... but it's much easier to tamp it flat/to the slow if you have some boards you can tamp along