You can weigh a 8 oz can of tomatoes or beans etc... to see if your scale is accurate
What type of hay are you feeding?
I don't think you'd be close to the 18% protein recommended for growing kits with the diet you described and certainly not with a grass hay, an alfalfa or clover hay would be a better choice to boost protein levels
And don't be too discouraged, if these are your first rabbits it will take a few generations to develop your bloodline to grow well on a non-pellet diet as nearly all of today's breeds are raised on commercial pellets and have been selected to decades to grow well on this feed
I don't think you'd be close to the 18% protein recommended for growing kits with the diet you described and certainly not with a grass hay, an alfalfa or clover hay would be a better choice to boost protein levels
And don't be too discouraged, if these are your first rabbits it will take a few generations to develop your bloodline to grow well on a non-pellet diet as nearly all of today's breeds are raised on commercial pellets and have been selected to decades to grow well on this feed