What you are hearing is the 'm' being pronounced twice -- that is actually correct.
In Polish you don't collapse all the similar consonants in a cluster into one short sound the way we do in English. Think about the word "baggage" in English -- the "gg" is pronounced as one "g". Or think about the word "button" -- only one "t" is pronounced.
Now think about "lekki" (light) and "leki" (medications) sound in Polish. If you don't remember, go back and review those lessons. You'll hear two distinct "k"s in "lekki", but only one in "leki".
Or compare "pana" (gen/acc of "sir") and "panna" (refers to the Virgin Mary in the Polish Christmas carol, "Dzisiaj w Betlejem"). The first time I heard a young girl singing the song, I remarked to a Polish friend that the "n"s in "panna" seemed so long... and that's when I finally realized that I was supposed to pronounce all the consonants, lol :-)