Hello, Anon! Thank you for posting.
In order to resolve the ulcer, more area may need to be removed. This doesn't sound unreasonable to me. As far as it being cancerous, you have only the biopsy results to go by. It's standard of care that anything that is removed, even in a second biopsy, should be sent to the lab. So you will (and should) receive a second report from the second biopsy.
If you feel uneasy or unsure about going back to the oral surgeon for whatever reason, you can get a second opinion. It's really up to you.