2 Bits of Advice:
1) I encourage you to keep going. Do not go back and start again. Rather, pick up where you left off and write all the way through to the end. Write early in the morning before the critic has awakened -- your beast, so to speak. Do not read what you've written.
2) Give yourself positive affirmations about your writing. Write them on post-it notes and post all over the house = on your bathroom mirror, the refrig, etc. Tell yourself:
- I am a great writer
- I enjoy the creative process of writing my thoughts down on paper for others to enjoy
- I marvel at my ability to fill up a blank page with valuable information
- I am grateful for the creative muse to visit me and inspire me and allow words to flow from me to the page.
Reprogram your belief system. Don't give in to the belief that you are not good enough, that you are not a writer or whatever else you are now currently saying to yourself. See yourself sitting down writing and enjoying the process, enjoying seeing the words flow, enjoying seeing your imagination become reality. Visualize this over and over and over again as you're driving, brushing your teeth, hanging out. Believe in yourself as a writer.
At first it will feel false, soon it will be real.
Turn off your critic. Allow yourself to be a true writer which means you appreciate the creative process and that the right words do not always come out the first time, that you cannot always convey what you imagine for your story the first time. Writing is a process. Get the words down. Later you can go back and be brilliant.
Finish first. Remember what you are good at. Forget everything else. Writing is all that matters now.