Confidence will come with practice, and just keeping telling yourself "the next one will be better, but I'm doing my best on this one."
A few other things to remember:
1. As was mentioned above, make sure your sandwich has no puckers , regardless your basting method. You can't fake that. Iron it all super flat and smooth from the middle outward.
2. You might "hit a wall" or get frustrated when you're quilting. Stop. Take a break. It doesn't have to be finished all in one sitting.
3. Use gloves. If you don't, you won't get a good grip on the fabric. I use cheapie garden gloves from Lowe's. Rubber palms provide some "grip" to the fabric.
4. You might have your doubts about how your quilt looks before it's done. Even those of us who've been doing this a have a moment in the quilting process when we say to ourselves, "What was I thinking?" Or "this doesn't look good" or "I hate this thing!" But after you've quilted it, something magical happens--you fall in love with it again. Sometimes you love it so much that, if you are making it for someone else, you might really be tempted to keep it for yourself. That's a great feeling!
And then, after your binding is on and you have finished your first quilt ever? That's a proud moment, mistakes and all! And you will be so eager to start your next one!