Going to second this as the best response. While high-quality chest compressions take practice, it isn't rocket science and even if someone had no idea what they're doing, anything is better than nothing. If someone's heart isn't beating their brain is dying by the second. It's not like if you did the worst CPR in the world you could hasten their rapidly advancing brain death.

To OP, I understand your frustration. I had a similar experience years ago. If you feel guilty, try not to. You did what you could with what you had. Thank you.