Can I back out of 1st time buyer real estate purchase?

Depends upon law in your state. Usually, you will lose the earnest money that you put down on the contract for sale, if you have no valid reason for backing out. However you state that seller changed closing date several times.....did you agree and sign an extension? If so, you are out of luck for the most part. However, if the delay has caused your costs to go up, perhaps the seller will give you some concessions to apply toward your increase in cost. It's usually better to compromise than to just back out, if it's a signed contract and you have the wherewithal to get financing. Usually, the financing condition you have listed doesn't list a specific rate qualification, unless you thought ahead to include that. Better to get some local legal advice from a real estate attorney in your area.