First of all, speak to the dealer. If you're polite and explain the situation, they'll be more understanding. You'll have entered into a contract to buy that car. Look into the terms and conditions of the paperwork you were given when you placed your order. You'll probably lose the deposit and, technically, the dealer might be able to pursue you for losses from the cancelled order. These should be minimal, though, as the dealer should be able to sell the car to someone else.

Coronavirus: Advice on buying, running and owning a car during the outbreak
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