HI Jessica,i just want to ask question if can we still backup after signing

You can cancel the contract within 3 days of signing it. If you cancel the contract within these 3 days time, then the seller won't be able to sue you. However, if 3 days are over and then you cancel the contract, then the seller can sue you for cancelling the deal.

I agree with what James has said. The 3-day cancellation clause is called a Rescission Clause. If you cancel the contract within this time period, then your seller won't be able to sue you.

Both your answers are incorrect and this is terrible advice. It is clear that neither of you are mortgage professionals

The 3 day right of rescission only applies to owner occupied refinances. If you sign closing documents you take possession of the home that same day. This applies for purchases and investment property refinances.

When you enter into a purchase contract you pledge earnest money. The earnest money pledges to the seller that you are going to make every effort to purchase that home. Purchase transactions include a "financing contingency date" which give the buyer the ability to walk away from the transaction and receive the earnest money back without penalties if they cannot secure financing. If you provided the seller with a financing commitment letter from a lender and then back out of the deal you will forfeit your earnest money and can be sued for breach of contract.

Next time you have a question regarding financing, contact your lender or a qualified mortgage professional. Do not rely on the advice of people who cleary know nothing of mortgage financing.