One problem is related to the overfitting. To avoid this, you should test with different level of the Soft-margin. In this guide you are going to find how to improve the overfitting: http://www.csie.ntu.edu.tw/~cjlin/papers/guide/guide.pdf
After you study the guide, if you need more help, you can go to this series of videos where you can learn how to perform SVM, then how to select the best K-Fold.
The videos are made in Mandarin but you could learn from them just following the process.
1. How to use SVM: https://www.youtube.com/watch?v=4GB5HVw0CuM
2.Determine the Best Parameters via K-fold Crossvalidation https://www.youtube.com/watch?v=MyywXRLuABg