Sometimes missing the melody string when I strum

Hello all. Beginner Mountain Dulcimer player. As I practice I find I am having a lot of problems, but top of the list is my tendency to often miss the melody string as I strum a note. Since I haven’t gotten to fingering chords yet that means the melody drops out from time to time. I’ve tried strumming in and strumming out but it doesn’t seem to matter. I believe I’ve positioned the dulcimer correctly and I’ve tried a variety of picks. My arm just seem to sometimes strum downward at an angle to the plane of the strings. 

Does anyone have any recommendations?