The spinning of the planet is something else than the centrifugal force: the spinning is because of the central heat of the planet making it spin around itself.
The sun's gravity is getting weaker by time because the sun getting colder by time... at the same time the planets are losing heat also and so they are more under the influence of the sun's gravity.
The centrifugal force is because of the Sun itself spinning around itself and so repelling the planets away, while its gravity force draws the planets to itself.
Therefore, in this case, t
he planets should get nearer to the Sun by time: because relatively the loss of the central heat of the planet is faster than the sun getting colder over time.
And as much the object is small, the more quickly it loses its central heat: like Mercury lost its central heat before the rest of the planets, then Venus lost it, then the turn will be for Earth to lose its central heat by volcano eruptions and emission of its heat.
http://www.quran-ayat.com/universe/new_page_4.htm#How_the_Planets_Will_Standstill