My machine uses needles that do not have a flat side at the top. If I put them in and they are off even a teeny tiny bit i have issues with thread breakage.
Try different patterns of free motion and different sizes. I still struggle with meandering (lines don't cross). But, I am really good at loopty loo stuff (swirls with loops, think coiled rope spread out on the floor). Hang in there. And, just like the other ladies said, relax and move your body. I liked the dancing analogy. If i get tense, my quilting gets herky jerky. Listen to some music, or better yet, sing a catchy song!
Oh, and, straight lines were really hard.
Have fun!