1, before work, before work, will the company do a background check on you? If that's the case, you won't be able to get through this half year, which means you can't join the job either.
2. The company doesn't do background checks. If you go to work smoothly, the problem will be even less serious. Personnel don't care how long you sent it. It's all automatic transfer by the company, and it will be crossed for you every month, only after you join the company.
3. If you are really worried, go to the Social Security Bureau now and hand in the months you missed, so it will be foolproof.