I had a microscopic stool test for parasites. Came back negative. I've had 2 done. What are the chances...?

I just want to know what the chances are for me to have worms when I had 2 negative stool results. I asked my doc if they were screening or microscopic and he said microscopic. Anyone know? I'm just worried cause I suffer from horrible anxiety and the photos I've seen online scare me to death!