Go to your FSDO and ask for a student pilot certificate marked "RECORD PURPOSES ONLY".
Reference: FAA Order 8900.1 Paragraph 5-344 B.
B. Endorsement Space Full. If the allotted space for flight instructor endorsements is full, and the student seeks endorsements for additional types of aircraft, issue a second student pilot certificate clearly marked “For Record Purposes Only.” The second student pilot certificate will have the same expiration date as the original. The original will be issued to the student and the copy destroyed.
I was going to say "get your damn ticket!!!" But then I saw that's 2.5 months out of your control; no sweat I was in that boat too! I'd ask your CFI, he's the one who has to make the endorsement so let him decide what to do about it (or do what Houston said above). Good luck and let us know when you get close to your checkride!