Sorry but you are out of luck,
BitLocker uses AES-128/256 (XTS-AES 128/256) which is considered a "safe" algorithm (https://stackoverflow.com/questions/16537418/how-secure-is-aes-128)
"Almost" knowing the password does not change anything for you decryption wise as there is nothing like "almost decrypted", either you have the password or not.
Letting people "almost" decrypt something with a password that nearly matches the correct one would be a major security flaw as it would give hints on the real password.
As long as you can´t guess the correct password based on that "almost" or provide the 8*6 number long recovery key you got during initial encryption you cannot decrypt that drive.