Congratulations!!
I'm glad that it was found by someone that actually knew what it was, AND had the brains NOT to kill it!!!
As far as male/female is concerned, yes it needs to be probed to be sexed properly. Unless you are quite proficient with probing or "popping" them, these actions are best done by a vet, which it may need to be seen by a vet just for a wellness checkup.
In my limited experience, it looks quite healthy; not fat or gravid, just healthy. Very sad that someone just abandoned it.

Just noticed that you joined today...
Let me be the first to welcome you to the forum!!