In fact you can download the form TM30 from the immigration website (2 pieces!) and fill it out yourself, as long as your landlord sign and stamps it. With that you can go to Immigration. Done it myself in Bangkok some time ago.
Speaking strictly legal, the immigration has the right to give you a shorter time to stay. BUT they will normally only do that, if you are already on their list or black list.
I remember a guy many, many years ago, who came with a NON-O but was told at the airport immigration, that he only gets 30 days and after that will be prohibited to enter Thailand again. There was some legal issue.
But in 99 % it is a mistake by the person manning the booth. Remember, they are doing that by the hundreds every day, so a slip can happen. That's why a check of their stamp is always the right thing to do. IF they stamped you a shorter term, then aks them in a POLITE way, if that could have been a mistake.
This situation of having somebody else being in the room only applies to single patient rooms. If there are more patients, then this does not apply.
A nurse is paid by the hour, expect in a government hospital to pay something like 50 or more Baht/hour.
The reason for this is, that a) people have been doing silly things, when left alone and b) they might need help, which requires somebody to at least call for help.
Banglamung hospital is not recommendable. Try Sri Racha, or university hospital in Chonburi, but be aware that Covid has restricted many hospitals in taking in "other" patients.