Hi HokiesBlade! Welcome to the mental institute, er forums
I don't own the Hinterland set (which is what you are using, I presume), but let's see if I can answer your questions anyways, using my amazing psychic abilities
. Please keep in mind that someone else may have to correct me here, as mentioned above I am just guessing as I don't actually own that set.
#1 - I would imagine that this hill is supposed to lay flush with the ground. It's possible that you didn't line it up quite correctly, which just comes with practice, or if you are using a high-water content glue it could be causing some warping. If the latter is the case, try using a glue like Aileene's Tacky Glue, or another tacky glue that has a low water content.
#2 - This one is somewhat harder for me to answer. Basically, I'm guessing that it could be one of two things. It's possible that it is there for variety, like you said, or it may be there to provide a double layer for extra re-inforcement. You'd be better to get an answer from someone who owns the set on that one.
In any case, welcome to the forums, and to the world of cardstock modelling.
Bow down in respect or a craft knife blade might fall from the sky and knock you senseless. 
