If you're like me, you finished grinding shiny pieces for Mr Krabs only to not get any achievement once you reached 100 spatulas. At this time this seems to be a relatively common issue that should be getting patched soon, but in the mean time, you can fix it relatively quickly.

So first of all check the achievements progress, for instance mine was stuck at 96/100 so i was 4 off. Now start a new save game.

All you need to do is collect enough golden spatulas to fill that last gap up! Just rush through half of jellyfish fields and you should be good to go. The bar probably won't increase count while you do this but once you collect the last one the achievement should unlock.