Why is the lab created crown placed not the same size/shape as my original tooth? What problems can develop?

Dental assistant had a lot of difficulty placing permanent crown. It is extremely larger than my original tooth. I was told the original mold was “cemented” aka unavailable for being resubmitted to the crown company. No adjustments are being offered at this time.still have pain & hot/cold issues.Temporary crown fit great in my original clear retainer. Dentist repeatedly reminds a root canal may still be needed-Dentist offered to pay for new (other company) retainer. What are my options now?