Don't worry about it. Everyone, and I mean everyone, fks up some times (tho in your example it's not actually clear whether it was your fault or not), right through to endgame content.
Sometimes you even have entire runs where you just seem to do everything wrong. The other night I completely missed a mechanic in A6S, died, accepted rez just as an AOE went off, rezzed again, ran straight into a mine and died lol. Sometimes just everything seems to go wrong, I find if I make a bad mistake I often "tilt" and am still thinking about it, making me make another one straight away!
However, I think everyone has these things happen from time to time, and luckily they are not so often. When they do happen, I'll readily admit "sorry guys, just an awful run for me there". When I'm in a party and someone says something similar, I have no problem and just laugh it off, as I said, I have them too sometimes. I actually see it as more of weakness on the people who come out with a string of excuses, blaming anyone or everyone else, RNG, lag, whatever... if you fked up just admit it and move on. I'm much more suspicious of people that come out with excuses that they are actually just a poor player, and will likely wipe us over and over.
It is all a learning process. Most importantly is knowing what you did wrong - was it literally just something you did wrong, eg moved late, didn't see something, or something that needs changing, eg tank pulling more/less, dps focusing one mob in particular or something. If you don't know what went wrong, and just make up something (dam lag again!) nothing is actually learnt and will probably just happen again
