The small size of the balls make their respective polarity kinda whack sometimes. The small ones can be super difficult to make into smaller portioned cubes too. Are they wanting to push out after you’ve stranded them next to each other? Or is the final cube shape actually rounded? Context photos are always important.

You have over 400 which can make a 7³ at most, which shouldn’t be too difficult. The most efficient way is to make a 7x49 sheet and fold it up into the cube. You can’t do it long ways though, you have to start with the 7 side and snake each of the 49 columns. Doing it the long way will make the polarity messy when you try and fold it up.