Quite reluctant to share my achievements sometimes as afraid of looking boastful. How do I "sell" myself the right way in an interview where I don't sound boastful but confident of my achievements?

Remember that the purpose of an interview is to show and assure the hiring manager that you are the right person for the job. This means your achievements are proof points and the only way to display your suitability and ability. There are ways to talk about your achievements without sounding boastful. Here is a useful article, highlighting six ways to promote yourself without being obnoxious.​​​