Hey so the ending squares can still be used vertically which is why they're there.
Example:
1 + 8 + 4 + 2 + 3 + 3 + 2 + 9
Here you could use the left side to do 1 + 3 vertically.
For a larger grid to prevent misclicks, try going to settings and changing the "grid size" setting to a larger option.
Hope this helps! Thanks for playing.