When you combine various EXP items you don't add bonuses, but multiply them (with 2 exceptions).
PBI's total value is 100%+200%=300%, Exp Potion or Scroll is 100%+50%=150%, Blessed Bottle is 100%+20%=120%.
So, 300% x 150% x 120% = 540%
Read
this guide and everything will be clear.