If I fail to register and did not collect any Goods & Services Tax (GST) from my customers, will my GST registration still be backdated?

Yes. You will be required to account for and pay the Goods & Services Tax (GST) on all your taxable supplies made from the date that you should be registered and to pay the relevant penalties. This is so, even if you did not collect any GST from your customers.

Suggested Readings

Does Singapore have any value added tax or Goods & Services Tax (GST)? What is an Out-of-Scope Supply? What is Goods & Services Tax (GST)? What is Taxable Supply?