Displaying decimal numbers on 2D array grid view

I am trying to create a 2D grid with the following features:

1. It will have more than 100 X and Y cells, so I cannot show them all on the screen. Therefore, I want the user to be able to slide it to see the rest.
2. Using text fields, the user needs to be able to enter some values and I want to display those values in the corresponding cell. If the user entered 5, then (X = 5), (Y = how many minutes have passed since the user started using the application.)
3. The user can also enter decimal numbers.

Except 3, I succeeded but I need help about entering decimal numbers.

Actually, I have something like this, but I would like to write on the lines that separate the cells. Because sometimes the user might want to enter, say, (5.3); and I am not sure how to display that.

I appreciate your help.

Reference I used: https://medium.com/codechai/flutter-grid-view-from-2d-array-5467e4da5243