There are 3 different outcomes for the fate of our universe:

if the average density is smaller than what is known as the critical value, then the universe will carry on expanding forever.

if the average density is greater than this critical value then the expansion will eventually stop and then contract in an event called the Big Crunch.

and lastly, if the average density is equal to the critical value, then the expansion rate will slowly decrease to zero. After this our universe will be a set finite size.