I only got one dose of the chicken pox shot as a baby, and i'm 18 now. should i get a second dose?

Yes.: The current cdc recommendation is for 2 doses, regardless of age, for anyone school age and older who has never had chickenpox.

Yes: It is recommended that you have a second dose because the immunity cna go away. So get the second dose. Chicken pox as an adult is not a nice illness.

Certainly: You may have been lucky & developed immunity with one dose, buy 15-20% don't & it is a horrible & potentially fatal disease in adults. Another option would be a blood test to see if you were immune & then decide, but that adds time uncertainty & a hassle factor. I'd just get another dose.