I would suggest riding centered on your board. If your board is directional, you're likely setback a little - in which case you can widen your stance a little - maybe 1 mounting hole out from where you are. If directional, move your front binding forward 1 hole, if twin play with to find a setting that feel comfortable for you. I think you'll find it a little easier to control your board with just a little more length in the nose than the tail.
As far as the difficulty of the runs/terrain, well I am an advocate for pushing ones self onto blues & steeper greens, as you'll be forced to put what you've learned into effect instead of just being "comfortable" riding something that you've come to know. The change in terrain is kind of like muscle confusion in a workout regimen. The more new/harder terrain you try to incorporate, the easier the stuff you know will become & you'll advance faster. However, don't bite off too much more than you can chew. It's ok to side slip a blue or steeper green the 1st time to feel it out, but try to make turns towards the bottom & then the next time going down it try to link turns as much as you comfortably can, even if it means side slipping halfway & then turning, until you're at a point where you can make turns the whole way down. This is a sport where pushing yourself (within reason) will prevent you from plateauing out & getting comfortable with what's easy & familiar. Don't confuse this with me telling you to push yourself to an unsafe riding situation, but more a friendly shove in the right direction