binomial expansion (3a^2-2b^3)^4

is this right?
(3a^2)^4+4(3a^2)^3(-2b^3)+8(3a^2)^2(-2b^3)^2+12(3a^2)(-2b^3)^3+(-2b^3)^4

81a^8+4(27a^6)(-2b^3)+8(9a^4)(4b^6)+12(3a^2)(-8b^9)+16b^12

final answer
81a^8-216a^6b^3+288a^4b^6-288a^2b^9+16b^12

No, the coefficients are

1 4 6 4 1

not

1 4 8 12 1