school bus endorsement with class a permit

Please help!

I got a cdl a permit and I got a school bus driver opportunity, they will train me for a class B or C.

I made an appointment to include S and P endorsement and the DMV said I can't do the computer test because I didn't have a CDL A.

I have all the trucking endorsement and they said I can't put more endorsements...

They even said to me finish all the processes and take the cdl a and then come back and do the endorsement, but I don't have money or time to first do the A and then try the B.

I don't want to lose this job opportunity! What should I do? Can I cancel the permit and start all over again with B?