Prove by mathematical induction that 2+5+8+...+(3k-1) = 1/2n(3n+1)

k^2 = 2+5+8+...+(3k-1)

(k+1)^2 = 2+5+8+...+ 3(k+1) + [3(k+1)-1]

(k+1)^2 = 2+5+8+...+ 3(k+1) + 3k + 2

(k+1)^2 = k^2+3k+2

k^2 + 2k +1 =/ k^2 +3k +2

Did I do something wrong or is the problem not true?