look i don't know you or your situation or what you want in life. in the past 13 years, i finished 2 years of a b.a., travelled and worked in japan, got married, ran a bed and breakfast, a catering company, waitressed, worked in a bookstore, moved 6 times, bought 2 houses, started a play group for moms and tots, became a board member of a non-profit family resource center, had 2 children, and now am chair of a fundraising committee. my husband among other things just started his own computer consulting firm, and he started out in biology at university.
you can analyze and stress and sweat over every decision that comes your way or you can embrace each new opportunity. you can't compare yourself to your sister, or what your parents hope for you. in the end it is your life. all i know is nothing is static and those you try desperately to prevent change and stay on the path, tend to be unhappy.
when i lived in japan, kids have to pick their extracurricular acitivity in grade 6, i think, maybe 7. that is it. they will play basketball or soccer or whatever until grade 12. they focus on studies so intently that their results from jr high determine the high school they will go to. it's very stressful. imagine making a choice and then that is it. they are discovering that these kids are actually experiancing a syndrome that is making them sick and possibly violent. change is good, variety is good.
so pick something and if it doesn't work out, it's ok. something new is always around the corner, if you are open to it.