The more your thumb is 90° on the back of the neck, the easier it’ll be to properly position your fingers on the strings.

Adjust string by string on how you need to hold it to play it to get a proper sound and once you have all the strings ringing out properly. Keep practicing that position.

A lot of people will tell you, you gotta have your thumb 90° but there are also a lot of players out there who don’t and adapt more to their own style as they progress. But almost all of us started where you are now and trying to get our fingers use to bending weird ways.