Coolant FL22

I just did the Coolant change for the first time. Used a gallon from a mazda dealer.

The reserve tank is low after using the entire 1 gal. Is there a way I can buy a smaller amount?

If I ended up buying another then it will be for another 5 yrs or so - storage space is also another issue!

Can I use this to top it off - Zerex 1 Gallon Green 50/50 Coolant/Antifreeze - it’s 5yr service - so I went with dealer part - but ...

Update - did some research
0000-77-508E-20 - premix - $25
0000-77-501E-02 - concentrate - $30 - Had I known, I might have gotten this. Now I need to find one + distilled water!
mazda 5
If you're going to end up with some on the shelf anyway I'd buy the concentrate. You can mix the correct ratio and still have the same size container.
2010 Mazda 5 Sport
Add distilled water or better yet, de-ionized water to top off. No need to have anything left on the shelf.

1 overflow tank of water is not going to change the percentage enough to say so.