I was running a Bolner OTK deck and when I went to pull off the combo, I used two Lightning Bloom at 10 mana but my mana didn’t change. I should’ve been able to go above 10 mana right?
No. Gain mana cards that grant mana like Lightning bloom (or biology project and floop in wild, etc.) cannot exceed your maximum mana pool which for non-druids is 10. The way to execute that combo requires you to play bolner first, then bloom, then y’saarj. I play that deck so I’ve had practice 