Of course, you should fill in your tax declaration in all conscience.
Be really careful with your income and assets. You have to declare every single item. If you forget to declare some positions of your income and the tax office discovers it, you probably will be accused of tax evasion. However, if you forget to declare a bank account with a low amount, there shouldn’t be any huge problems and there are a few ways for you to fix it.
In the case of deductions, it is usually much easier: the tax office just cancels all deductions you are not really eligible for and estimates your tax payable based on its own calculations. You won’t have to pay busses or other penalties for this. The only thing that changes is your tax burden. Since one or some deductions are canceled, your taxable income will be higher. Thus, your tax bill will be also higher.