Check your credit report carefully to make certain that there are no mistakes. It's a good idea to get copies from all three companies to assure there are no mistakes since any of the three could be providing a report to your lender. Simple mistakes are easily corrected by writing to the reporting company, pointing out the error, and providing proof of the mistake. You can also request to have your own comments added to explain problems. For example, if you made a payment late due to illness, explain that for the record.
Lenders usually understand that legitimate problems sometimes arise.
A credit bureau score is a number that is based upon your credit history. Your score is used to determine whether or not you will likely repay a loan. Lenders use it to determine your ability to qualify for a mortgage loan. The better the score, the better your chances are of getting a loan. Ask your lender for details.