I would suggest you to keep trying and get all the documents before 20th. You can always decline the ITA right before it expires if things don't work out. I'm assuming you have 800 CRS points at the moment and you probably will get an invitation on every rounds from now till march. You can chill, but it's never a good idea to postpone things and hope for the best.
If the only thing missing is the letter from your employers, give them a PHONE CALL and tell them its urgent. One of the most crucial and hectic part of the application process is this time between ITA and AOR.
I will list down the required documents and the key information that these documents should have.
EDUCATION : All your degree certificates, transcripts, ECA report and language test results
ID : Passport
POLICE CERTIFICATE : police certificates of all the countries you've lived in for more than 6 months
MEDICAL : medical certificate from any of the approved panel physicians in your country
PHOTO : your photograph
WORK : letters from your employers on official letter heads including all the given info (Role, Duties and responsibilities, Employment dates, Work hours in a week, Annual salary, Job status(if current job) and Company's contact info with signature and seal)
PROOF OF FUNDS : documents from your bank showing the required funds (for eg. $12,000 CAD for single applicant) with other supporting supporting documents to show that you've had this fund in your account for the last 6 months. Don't worry if you didn't have the funds 6 months prior to this, there are bunch of other ways to support the proof of funds part. It varies on everyone's case. I can guide you a little bit if you can give me some more information such as if you're planning to show the funds in a savings account or fixed deposit. You can also start reading many other threads in this website about the proof of funds posted by senior members such as Asivad Anac and Anujgupta.
Hope it all works out quick and easy for you.
Best of Luck!
My AOR is 19th dec pnp outland 
