On top of what others have said …
Neck dive can be a factor. If your fretting hand is having to hold up the bass while playing, that’ll stress your wrist too. If your bass has noticeable neck drive, try hanging some weights off your strap at the bottom. Nothing too heavy. And don’t be afraid to use something weird like a bag of coins. You’re just testing to see if it helps, you can change it later.
Neck angle matters too. Pointed higher towards the ceiling and more parallel to your body makes the low frets easier to reach, while pointing more horizontal and tucked in closer to your body makes the high frets easier to reach.
I’ve always been more comfortable standing while playing. I barely use my guitar stool anymore. But you might want to try “classical position” while seated:
I know this seems like it will make the low frets even further away, but the neck angle helps bring it in, and the position overall helps keeps your wrists straight.
You just started a few days ago, right? You will definitely get used to it the more you practice.
The problem is that “playing bass” is actually like half a dozen or more different skills at once. Holding the bass ergonomically is one. Fretting is another. Plucking is a third. Muting, fourth. The basics of rhythm, fifth. Keeping the exercise you’re working on in your head as you play it, sixth. You can’t consciously think about all these things at once, so whichever one you’re focusing on, the others will suffer.
The solution is to just keep at it. The more you do these things, the more they will shift into your subconscious, or “muscle memory.” And every time a skill transfers into muscle memory, that frees up your brain to think about another skill.
Try to go through at least half the course before deciding, if not the whole course. Worst case, the refund policy is very generous so you have plenty of time.