When you have slipped up, don't be critical of yourself. Nobody is perfect, so if you try for perfect, you set yourself up for failure. Don't try to make up the difference. Just jump back in where you are, and get back on track.
Remember, two steps forward and one step back is still one step forward. As long as you keep moving forward, you're winning. No one is perfect -- forgive yourself, learn from your experience, and soldier onward.
Setbacks and mistakes are a very important part of living and growing. It's one of the most effective ways we learn. Don't dwell on them. Briefly study what went wrong, and move on, tweaking things a little to find your next good groove.