Hang in there. The only thing that surprised me a bit in your post was the saturation going to the 70's, but even that not knowing the whole story I wouldn't judge you. If the patient was asymptomatic completely for example you might have incorrectly assumed you could wait to sort out why he was sat'ing that low. I had to chuckle though at the new grad nursing student who said this
" We were given 15 minutes at the beginning of each clinical to meet our patient and review the chart."
I really think right after nursing school you have to hold off giving advice to RN's until you are working on the job and see what the real world is like. there is no 15 minutes/patient at the beginning of the shift to review the chart, that is nursing school only, you can take 15 minutes or as long as you need obviously to assess your patient and read the chart, but with 6 or 7 patients, it isn't always possible to get that all done at the beginning of the shift. That said you get better and better at getting a handle on the patient and being ready for report etc as you get experienced. I have only been on the job about 3-4 months without a preceptor and it is getting better everyday.
Coincidentally just the other day a Nursing student casually came up to me to tell me my patient had an O2 saturation of 75% at which point I jumped up went in the room and he looked better than ever so I took a deep breath and said 'Where is the vitals machine?' She said 'Oh, I gave it to another nursing student'.. I quickly got another one, confirmed his O2 saturation was 98% and then gave her some education on how to handle the whole thing properly and how O2 saturation in the 70% was critically low.