Why is my voice like this? How do i fix it?

Well I was bored and i didn't have any thing better to do so i started to see how far up my keyboard i could go...and i can do one octave below middle c, all of middle c and then the octave after middle c was "broken(lets put it like this)" and then after that i did the c two octaves from middle c, but i can't do the between one... so how do you fix your bridges? I guess that's what i am trying to ask...I mean i feel like i am trapped in a bubble and i want to use the high c when i sing this song for my school talent show, but i am afraid that when i get on stage i won't be able to do it right cause my bridge is weak...so how do you strengthen your bridges? Thanks to you all for any advice you have to offer... =)