At least you have a start there. 90% of newbies buy similar. That bike is made for fooling around on MUP trail hills. It only goes 20 mph max with those 34/22 cranks. It will take a long time until you get lighter and faster. Hopefully you live where it's not cold and winter soon, like here. Pffft
Your sore neck is because of that pathetic straight broom handlebar. ZERO comfort change positions. It needs a bar with sweep back, the more the merrier in my case.
Anyway, it's hard to have a fast avg. when not on the highway. For me anyway.