Is it possible to perform a contactless transaction with my VeraCash card, without realizing it?

No, you cannot make a contactless payment unintentionally.

You are the one who initiates the payment by bringing your card within 3 or 4 centimetres of the shop’s payment terminal to confirm the amount shown. Farther away than that, your contactless card cannot confirm the transaction. This keeps you in control of your contactless payments. In addition, all contactless transactions end with a receipt being issued.