Ask away. We all love quilting way too much not to share ideas.
A few things to take into consideration:
1) Is your practice sandwich made with the same type of fabrics & identical batting to your actual quilt? If not, be sure to do that.
2) It would help to share what kind of fabric, batting & thread you are using. I am most familiar with 100% cotton quilts, so my advice is primarily based on that.
Here's what I would check (note: all this advice is for newbie quilters; it is
not the only way to do things, just the easiest):
1) Use 100% cotton thread in the top & bobbin.
2) Check your threading. Cut the top thread by the spool & pull down from by the needle. This will "floss" your thread run in case there are teeny little fuzzies that might be caught. Also, honestly, I'd try filling & threading a new bobbin... especially if your bobbins are plastic as those can get warped & cause issues. And apply machine oil as directed in your owner's manual. For my classic Singer, I have a place in the upper thread run & the bobbin case that I oil. For my Bernina, it's only the bobbin case that gets oiled. I oil my machine every time I put in a new bobbin.
3) Check your settings. For straight line quilting, I use a Walking Foot (or you might have a machine with Dual Feed), set my stitch length to 3mm, straight stitch, center position, with a top tension of 3 & feed dogs are UP. For free motion quilting, I use a Darning Foot (also called a Free Motion Foot), set my stitch length to 0, straight stitch, center position, with a top tension of 1-2 & feed dogs are DOWN.
Note: depending on the machine, some people may work with the feed dogs up & find their machine does better. I personally would not ever set my stitch length longer than 0 with the feed dogs down; there is nothing to move the fabric but you.
3) If the "bird's nests" are forming (or thread is breaking) when you are going around curves, you need to practice matching your hand speed with the speed of the machine. There are two ways to do this. You can either keep the machine at a slow speed & slow down your hands moving the fabric, or my preference is to slightly speed up both the machine & my hands while going around the curve. I prefer that because I have difficulty producing a smooth curve at a slow pace. Marking your quilt helps, but there really is no substitute for practice. You're going to be ripping out some of the stitching around curves a number of times before it starts to come together for you.
4) Use the right needle for the job. For straight lines, I prefer a Microtex/Sharp needle, but a Topstitch also works nicely. For curvy lines, you can't beat a Quilting needle. It is especially designed with a rounded tip that helps the stitches form nicer & reduces problems when going around curves.
5) Set yourself up for success. There are fewer problems the wider the base is around your needle. Cabinets are great, but my first set-up was Whitman's chocolate boxes & one shirt box that I used masking tape to attach around the bed of my machine (yes, I made the sacrifice to eat all those chocolates in order to benefit my quilts
. Machinger's gloves or something else that's a bit rubbery make a huge difference. You can cut the fingers off rubber gloves or use those Secretary's fingers that they sell in office supply stores instead of the gloves -- or there is this tacky hand cream that helps. Any one of those options make a difference. Also, if you already invested in a Supreme Slider (or something similar), make sure that your feed dogs are DOWN. Feed dogs will chew up the Slider & you'll mostly end up stitching a nest in place.
If none of that helps, I would wonder if perhaps my machine needs service. But I think that's a little unlikely since you said your practice sandwiches keep turning out fine.
Keep working at it. And maybe adjust your deadline. I know what it's like to feel that pressure to finish something brand new within a week. It makes it really hard to be successful. Quilting, especially FMQ, is all about rhythm -- knowing your machine & figuring out how to work with it. I hate having to tell people I need an extra week or two, but the reality is that quilting takes time & that extra week or so can mean all the difference between a family heirloom and a tangled mess.