fingers not working like they should - sometimes

I am having two problems learning the dulcimer. I am teaching myself from your wonderful collection of videos, Utube and a book.

1. Just upgraded to a 4 string from a 3 string and seem to be rolling the 2 melody strings together more than I like - I'm trying to bring finger tips straight down while keeping them bent 2nd joint - hope to learn cords in the future.

2. I seem to have problems at the 10,11 and 12th frets by either club fingering them or shortening the strum and missing the bass string altogether. Don't have the problem with the lower fret numbers.

Is thiscommon when learning to play? Occasionally thougheverything comes together and the cats will stay in the same room I am practicing in. Thanks to any input anyone offers