Trying your best IS expected. If you need more instruction or time, simply speak to the instructor. Also, seeking help from the high belts can be valuable, not only for their technical assistance, but for the re-affirmation that you are not the first person to face difficulties. I can' t even touch my toes. Try coming to class on a regular basis or working out and stretching at home.
Different people have different amounts of static and dynamic flexibility.
There are black belts who can't touch their toes, yet can still execute mid-air split kicks. Your flexibility will increase over time. Tests are generally held 2-3 times per year. The more you come to class, the more likely you will be ready to test. It takes approximately 4-5 years under Terence Spielman to reach first degree black belt.