you took the job on 10+2 certificate.ok.
It also appers that your attendence of btech. was complete that is why they allowed you to write the exam. your beteh.decree is valid in my considered opinion.
There is no problem with current job if you have taken leave to write btech. exam with permission of your departmental boss.
You have right to appear in any exam based on your graduation decree of btech. for which there is no bar on you.
BUT PROBLEM may arise with respect to your PRESENT JOB if you have written eXam Durind a medical leave or or other ground as if they come to know and do not ignore they proceed to show that you have MISCONDUTED and they may proceed to enquire after a show cause notice to you that why should not a departmental enquiary be setup agaisnt you for you took the leave on a false ground and mis utilised it for writing the exam,which may result as a stagima to your condut.
If you have comitted a mistake of this kind,as my experience smells it,you are advised to go cool, appear in exams cooly ,if ,no department permission is required therefor,and when got ,selected,regine from this job.
The next thing is that if you are failing to mannage this kind of fear but have confidence to sail the compete the exams you want to write,just regine this job, forget every thing,and get sellected for the job you are desirousof.