Expanding each term:

(3a - a^2) - a^2(a-2)(a+2) + 2a(7+3a^2)

= 3a - a^2 - (a^2)(a^2 - 4) + 2a(7+3a^2)

= 3a - a^2 - a^4 + 4a + 2a(7+3a^2)

= 3a - a^2 - a^4 + 4a + 14a + 6a^3

= 17a + 6a^3 - a^2 - a^4

The simplified final expression is:

6a^3 - a^4 - a^2 + 17a