Vegan accidently eating ranch dressing?

i just became a vegan and today at lunch my mom ordered me salad with ranch, she told me vegans can eat it. so i did. and now i feel awful relizing its not vegan. ill never eat it again. but has anyone else whose a vegan ever accidently eating something they tohught was vegan but wasnt? how can i be sure of whats vegan and whats not? are there any salad dressings that are vegan? can i start fresh with veganisim tommrow?