Why are my buds so small?

Crappy autoflowers.......over feeding will cause excessive leaf growth at the expense of flower growth. Reducing the lighting levels is also a cause........blast them with 100%!

An overfeed of N will decrease de bud density.

I guess some Pk is missing.

If you'd like to simply your entire grow check out npk raw bloom. Every mineral and nutrients t has been ratio for perfect growth.

Your feeding alot, overdrive along with resin enhancers should only be used last 2 weeks. Overdrive has high levels of magnesium and potassium which you are already applying a cal mag suplement every week of flower. You should need cal mag maybe only 1 time pre flower and once maybe halfway through flower. When your plant is dealing with a overabundance of nutrients and minerals it doesn't need it can severely interrupt with plants ability to uptake other nutrients.