If this 13 year old kid with small 13 year old kid hands can reach, you too can reach.
Most 4 string basses have at most 19mm between strings. That means the D string is only 3.8 centimeters away from the E string. The G is only 5.7 cm away. That’s 2.25 inches. I’d put money on the fact that your hands, thumb to finger tips are longer than 2.25 inches. Even with your thumb anchored, you can move your hand downward and reach the G string.
But if you just got your first bass, just keep practicing. It’s not something that’s just gonna be easy in a couple weeks. It’s a lifetime of learning and improving, which is why it’s so fun and rewarding. So don’t be discouraged. Practice. If lessons are an option they usually help. There’s a lot of great instructional videos on YouTube. Scott Divine’s bass lessons are a great place to start. (Be careful, like everything these days, there’s also a lot of garbage and misinformation out there.) Experiment with different hand positions too. Try anchoring your thumb on different strings as you play the higher strings or floating thumb or resting thumb over the strings. (I think Scott’s YouTube covers a lot of beginner hand positions too.) If its still physically not possible for you for whatever reason, try playing with your thumb or a pick.
And most of all don’t give up. It’s a process.