New BP owner.

[Daigga]

As everyone has already said, remove the heat rock because they are dangerous and are known to burn animals. I'm not sure what species a heat rock is made for, but it's definitely not a ball python so see if you can get your money back for it

They're not good for any species, reptile or otherwise. They're made by people who thought it was a good idea and continue to be produced because the pet stores still somehow manage to sell them to people without properly warning them. Same things go for certain bedding materials, really (ie. crushed walnut, which is advertised for beardies, but is essentially a death sentence).

The the OP; Don't get overwhelmed, now. I noticed this back when I had an iguana on a different site, but it can seem sometimes like the people on forums like this are almost attacking you for some admittedly beginner husbandry errors, but that's not how it is. Everyone wants to see every animal happy and well cared for, which is now your responsibility as an owner. Take a deep breath and every piece of advice given with a grain of salt, and just know that no one is trying to attack you.

On to some more positive things! Keeping reptiles on a budget is totally doable, so long as you have your priorities straight. Firstly; a thermostat has to be high on your list of things to get. A burned snake is a very bad thing. If you can take the heat rock back (as this is more likely to burn your snake than an unregulated UTH) and get a refund, that should at least put you in range for some of the thermostats they have in the petstores (usually kept in the same areas as the heat rocks, you can get a cheap one for around 35 dollars). Second! Mouse fuzzies are way too small. I did this with my first as well, and I had bought myself a bag of 50 of the damn things when I got her. Bump up the food sizes, mouse hoppers or rat pups are ideal, though if you have bulk fuzzies like I did you can try feeding two at a time. I know someone said a secondary hide isn't very important, but a 55 gallon tank is pretty big for a snake that small, so I would say go for it. The same kind of wooden hide there is probably your cheapest option, plus they're generally available in bigger sizes than the rock looking ones, though you'll learn they are a pain in the ass to clean (Spot clean all the time, you'll thank yourself for it). Also if you can manage it, some extra decoration (foliage, driftwood, etc) would help your snake to feel a little more secure, as little snakes in big tanks tend to stress out.

In that order:
Heat regulation
Properly sized food item
hides and decoration

While you're doing all this, browse the forums and look up some videos of BP keepers. The more you know about your little one, the better off he or she will be. Also at your original question about telling gender; unless your planning on breeding, the gender is whatever you think it is (read; it doesn't matter, and finding out can be stressful/unnecessary for a pet snake).