Hey, no problem! We all starts somewhere so dont get too harsh on yourself! You will gain more experience and learn from past mistakes as you participate in more game jams so I would suggest you to join more game jams whenever you are free to sharpen up your skills!
I am also a solo dev and am a complete beginner at drawing since im not really an artistic person so what i do is i just search whatever assets i need from the web (but remember to credits them accordingly!) and use them instead of creating myself. Mad respect that you are able to create the art on yourself tho!
Hope to see you in some other future game jam! 😉