When you make a formal offer on a house, your contract should include a financing contingency. It specifies if you don’t get the money you need to purchase the house at the terms you want, the offer is void and you will be refunded your deposit.
Don’t be surprised if the seller includes a clause in the contract that states you must make a “good faith effort” to get the mortgage. This is the seller’s way to ensure that you explore all options to get a mortgage loan.