Feeling anxious while meditating can be a sign that you're trying too hard to meditate "correctly." In other words, when you force yourself to sit still or try to stop thinking, you tend to actually cause strain, anxiety, and tension.
So, see if you can let go of trying to control your meditation experience, and instead just relax and accept whatever happens.
If that's proving difficult, you can try doing something you enjoy—like taking a walk or listening to your favorite song—for a few minutes before you meditate to help set a more relaxed and playful tone for yourself.