In the first instance, we'd recommend speaking to the dealer. It's unprecedented times but they should do everything they can to help. They might offer a loan car until your car arrives, or find a similar one in stock. If you do want to cancel your order, it's down to the terms and conditions in the contract you signed when you placed the order. It'll probably say the three months was just an estimate and it could take longer - meaning you won't be entitled to a refund. If you remain polite in dealings with the dealer they might return your deposit.