There are an infinite number of numbers between 1 and 2. Infinite doesn't mean boundless. So if you had a number line, and you place an infinite number of points on that line, you could then extend that line to be between 0 and 3. There would still be an infinite number of points, but those points would be further apart.

Likewise the Universe is infinte in time and space. There's always more time, more space, but also the time between points in time can grow and shrink, and the space between points in space can grow and shrink.