Usually we don't respond to requests for tax advice for
salaries under CHF 3 million, but since you're new 'n' all ...
You are required to fill out a tax return (thereby enabling you to claim any overpayment of tax) if you earn more than CHF 120,000. I don't know what happens if you earn that salary pro rata, but haven't earned a total exceeding CH 120k in the year. I suspect it's not good news, unfortunately ... sorry! All I can suggest is a phone call to the tax office.
Good luck!