You don't need a long arm to do amazing quilting, I promise...you just need practice. If you're free motioning, you might need a bit extra.
First - make sure you've pinned, A LOT. From the picture it looks like you need a bit more. I would pin every 2 inches on a big quilt like that to ensure no wrinkles get sewn in.
Next, as others have suggested, roll the edges of your quilt and use clips to hold it in place so you're not struggling to fit your quit in your machine instead of focusing on your sewing.
Third, if you're sewing in the ditch or straight lines use a walking foot, this will REALLY help prevent wrinkling. It will also come in useful when you attach the binding.
Fourth, if you're free motioning, expect there to be a learning curve. I consider myself fairly artsy fartsy and it still took me a while to get free motioning down. Start slow...and it helps to practice on smaller projects first.
Fifth - make sure you use the right needle with the right materials. If you're using the suggested (to start at least) 50 wt. cotton, I find using a quilting (or topstitch) needle in a size 14 works best. You also want to play with tension, you usually need a higher tension when free motioning with cotton than other threads, even higher than what you normally use for piecing with cotton thread.
I promise, with some practice you do NOT have to resort to a long armer. If you want to - there are tons out there who would be happy to quilt your top for you, but I promise having a long arm is NOT the only way you can achieve great quilting even on big quilts. :)