It is possible to contest a will, but not because you feel you didn't get your share; you have to have reasonable doubt about its legality.
Fraud or forgery are two valid reasons but both are not only difficult to prove; they can also be very costly.
If you feel you want to contest a will, seek legal advice immediately. You only have six months in some cases (depending what grounds you are contesting on) and you will need to be aware of both your chances of winning the case and how much it is likely to cost.
After all, there really is no point in contesting a will in order to get more money, but then have to pay out double that amount in legal fees.
Please check the legalities in your own country as obviously things will differ, but your first port of call is to seek legal advice on whether it is something you can pursue.
Good luck, I hope you get what you are entitled to.