Obviously there's not many UI/UX experts here, try seeking help on a design forum or something more suited to this exact problem. Some general things to consider when it comes to buttons and UI:
Shape,
Size,
Rendering,
Font,
Icon
Shape - you're using a classic rounded lozenge shape, that's fine - does the job, doesn't say much about your game, maybe that it's cute, soft etc. Be more consistent though, the top left counter thing has more flattened round corners instead of full circular ones. A stylised envelope shape might say something more about your game but might be tricky (remember that's not an 'icon', it's the button itself, icons are for communicating function like your back and pause buttons).
Size - remember hierarchy (main options big), don't have anything small and fiddly - especially on a touch screen.
Rendering - generally want buttons to look inviting to press down, should be immediately obvious, the shinier ones work for this, I'd do it cleaner, maybe a border etc. Colour is important, try and make consistent and meaningful choices (ie. confirm / cancel being different colours). Just cos your game is pixel art, doesn't mean your UI has to be btw, there's a benefit in vector art for this kinda stuff if you're targeting different screen sizes.
Font - this is what's killing you, that font is atrocious. Say something about the game that is deeper than "This is retro cos it's made of squares". Again make consistent and meaningful choices, keep to as few fonts as possible over your whole game.
Icons - Current thinking is abstract associations are 'bad' (eg. the once commonplace floppy-disk), but it's up to you if you think there's a communication benefit. Some icons are more recognisable than others (I don't like X as it can mean close or delete, tick can mean confirm or done etc etc. Make sure there's accompanying text when there's any ambiguity). FontAwesome has some nice one-colour icons, free to use.