As first blush, it would apper that thsi sitaution appeaars pretty grim.
First thing wopuld be to contact a good mor5gage broker. They would be able to advise you of your situation. Also, a GOOD broker can counsel you & tell you what you need to do to get that score up to an acceptable 600-range. I(f you do not know a mortgage broker, I can refer several reputable lenders that will assist you in this effort.
Second, I would review the documents that you signed earlier. I would ask an attorney to review them for you to see if you have any options,
Third, I would ask the landlord for an extension on the deadline. I would want to shoot for a new deadline after reviewing your options with a mortgage broker who should be able to give you a deadline for the repair of your credit history . It may be in everyone's interest to work together make this deal work.
If I can assist, drop me an e-mail at firstname.lastname@example.org or call at 440-487-2193.