It takes tons of practice! We have a longarm gal in our guild and when I look at her quilts, I am amazed. She has done over 3000 quilts! That's right 3000.
I've done maybe 20. Why would I think that mine would look anything like her work!? My point being, relax and enjoy the learning process. Do a couple of dog beds quilts. Just put some muslin on, with batting and backing, watch some videos on YouTube and practice, practice and practice some more. If you don't have dogs, donate the beds to your local animal shelter.
You may have to adjust tension, and that's OK. Get to know your machine before you expect expert results.
I still have to adjust my mnd before I start working on a quilt.
Relax and don't be so hard on yourself. It will come together, it just takes time and practice.