Similar question that someone else posted about egentlig -- originally and actually could have pretty different meanings. Perhaps the answer here again is context, but what sort of (well-intentioned) follow up question would help to clarify in this example?
I would simply ask Hva mener du med det?, what do you mean (by saying that)? I think that is a good open question where you can invite the other person to elaborate.
I'd be careful not to intone any words stronger than another though, putting stress either on mener or det quickly comes off as rude and signaling you already have a strong opinion on gender issues (or have quickly decided you don't like this person (anymore)). Being a foreigner you will have lots of slack on the intonation thing, so don't worry too much about it.
originally - opprinnelig. opprinnelig and egentlig do not mean the same thing.
This might sound stupid here, but i keep getting confused between 'jenta' and 'jente', can someone explain the difference for me, please?
I put "i'm originally a girl". I realise actually is the more usual translation, but is originally wrong (as marked)?
Well, I haven't tested it, but it definitely should. Originally implies that you were a girl some time, but no longer. Actually implies that the other person may think you're a boy, but you are in fact a girl.
I think it is wrong since if anyone wanted to add this being born as bit they would have used unambiguous 'originally', one which had been mentioned above.