blend space not in even

steps i followed

1.draw rectangle width 700mm x 600mm

2.make it rounded rectangel

3.contour the object inside with 10mm  & break it

3.draw 5mm filled circle and fit it on outer rectangle with bled option with 5mm space

4.draw 3mm filled circle and blend it & fit on inner rectangle

5. on some part the 3mm circle align centered with respect to outer rectangle 5mm circle

i need inner circles equally spaced .please help

sample

O   O   O   O   O   O   O   O   O  O  O  O  O  O  O  O

   O   O    O   O  O  O   O  O  O  O  O  O  O  O  O  O             --> these are not aligned

i need

O   O   O   O   O   O   O   O   O  O  O  O  O  O  O  O

   O   O    O   O   O   O   O  O  O  O  O  O  O  O  O  O             --> these are not aligned