Coffee

I posted recently asking how to make a good latte, made this one following all of your advice. Here's what I did:

1. Measured out 15g of espresso ground (from a pre-ground source). Was shooting for 18 but the porta filter ran out of space. Credit BurntWits.
2. Tamped it down a bit at first to get it spread evenly as I could, then hard into the portafilter per SreudianFlip's instructions.
3. Pulled the machine from storage, placed portafilter into the machine, then turned it on to the double shot mode (it's set for 25 seconds).
4. Realized I forgot to put in water (it was stored dry), filled the reservoir with water and waited for it to cool down.
5. Repeated step 3 with the same puck (hey look at me, im using coffee lingo). Tried getting it to 30g of espresso (credit Micromot for 1:2 ratio), but messed up the timing and accidentally got 51g espresso. Don't recall what time I stopped it at; I just turned the machine off when I hit just under 20g and I guess it ran for a bit longer. Espresso went into a ceramic small bowl.
6. Measured out 150g of cold 2% fat milk into a ceramic mug to steam (credit some probably AI generated website for 1 oz espresso to 5 oz steamed milk [yes the website used oz and im working with g, there's probably a difference but to be honest with you im not sure how to do the conversions {that's a lie im a CS major with an interest in physics and a person with access to the internet, I probably could have done it, I just got lazy}]. The ceramic mug used for steaming was different from the one used for drinking). Steamed milk, forgot to put in flavoring, added chocolate chips (tiny semi-sweet) while steaming. Ended up steaming for 65 seconds.
7. Poured espresso into pictured mug, added milk on top.

It came out... meh. Bit bitter; unsure if that's from the milk, the chocolate, or the espresso. Added an amount of sugar and it was better. I have a suspicion it was the chocolate chips.

Thanks to Burntwits, Micromot, Robin, AngryishHumanoid, and SreudianFlip for your comments and help! I quite appreciate it, and I hope my next one turns out better.

Ive learned 2 things about my machine. 1: When pouring, pressing the power button will shut off the process, but whatever water already in the process will keep running (I think) meaning to get the desired amount of espresso I have to time it right. 2: I can program the timing, but all this means is the machine will run like normal, except the timer will count up instead of down. I guess this means that the next time I use the double shot (DS) espresso mode, it will run for whatever amount of time it recorded when I last programmed it. I don't know if DS mode actually does anything different from single shot mode besides being a second preprogrammed timer to run the pull for.

Tools used: Two ceramic mugs for steaming and drinking, small ceramic bowl for holding the espresso temporarily, my roommates weed scale (I think its intended for food. nothing made direct contact except the ceramics and portafilter), 2% fat milk, x branded Semi-sweet mini chocolate chips, y branded 100% Arabica espresso grounds, z branded espresso machine and accessories.