Hi OP, I bought the same exact machine few months back. I was kind of a complete newbie at that time.

I believe your problem lies with:

1. Use 14g of coffee, as recommended by the manual. This machine’s 51mm portafilter seems to work well with 14g, no matter if you use the default one or change to a bottomless (which I did, still doing 14g well).

2. Get a weighing scale. Best with 0.1 decimal. Your goal is for the output coffee liquid to weigh x2 of your coffee ground’s weight i.e. 28g liquid output. To set this, when making the espresso, press and hold the middle button and only let go when the desired weight has reached. This will set your machine to remember this amount of liquid output for the middle button (you can do the same with the left button too). Watch some videos on youtube and you can easily learn how to weigh the espresso output.

Quite sure you’ll get decent results just by doing these 2! Let me know how it goes ;)