Virtually everybody's first few 6s games are train wrecks, even in low-skill environments like Newbie Mixes/Lobbies. Many of them have the right DM, but none of them have experience and so they often lack confidence because of that. My advice is to just do it. The first few games will help you overcome an experience and confidence barrier even if you suck, as long as you get feedback (Newbie Mixes are the best for this).
As said above, another thing you can do to improve outside of playing the game is practicing your mechanics in MGE/DM/jumping or trying to gain knowledge by watching matches on streams/demos.
(Also, 6s skill transfers into Highlander better than Highlander skills into 6s, usually).