These are things you should have sorted out before joining. It is not really the recruiter/guard's responsibility to tell you about the other branches.

As to getting your MOS/Ship date changed, it is "possible" but not "probable". No one held a gun to your head and made you agree to what you committed to, so therefore you are expected to completed what you agreed to do while at MEPS.

You have done a great thing by joining, you can now make the best of your decision and learn all that you can, so that you can be proficient as a Soldier in the career path you have chosen.