cosmology - Contractions between big bang and gravitational law

If big bang happened then the centre of the universe must be place of big bang.

Let the mass of whole universe be $M$ and mass of small planet or any Astro object be $m$. Then the Gravitational force between $M$ and $m$ be given by:- $$lim_{M\to\infty \, m\to0\, r\to\infty} \frac{G_\infty M m}{r^2}\left(1+\left(1+\frac{r}{\delta}\right)\alpha e^\frac{-r}{\delta}\right)$$

Where $\alpha$ and $\delta$ are constant.

Then according to the gravitational law ,, attraction force on $M$ and $m$ must be equal. Then the acceleration of $m$ will be infinitely high towards $M$ as compare to acceleration of $M$.

Then by this theory universe instead of expanding must be compressing and the shape of the universe must be sphere "if big bang theory is correct."

I want to know whether I'm Right or not.