B. I want to go to the concert, but I'm not sure if I will be able to make it to see the beginning. is your best answer.
There are two sentences that are being combined:
"I want to go to the concert."
"I'm not sure if I will be able to make it to see the beginning."
Because the second sentence is conditional, you must use "but", as a conditional word to make the sentence correct.
Hope this helps