struggling ICU nurse

[lizdimi54873]

Would love some advice! 
I have been in a level 2 ICU since early this year. I transferred from a specialized ICU in a different state where I worked 1 year. Before that I had 2.5 years of med surg experience. The ICU I'm in now is mixed. We get cardiac surgery, open hearts, trauma, GI, dka, pulm, neuro/stroke, pretty much everything. It's been challenging because I'm per diem and also because a lot of what I'm seeing is new to me, especially in the ICU setting. My old ICU was trauma/surg/tranplant; any cardiac or neuro we sent to other icus. Basically, I'm wondering if it's normal for me to be struggling or if possibly I need to rethink my speciality. Things I love about the job are that we have a lot of experienced nurses around who are a wealth of knowledge. Also, the per diem flexibility has been exactly what I need. However, I feel like being there once a week makes it difficult to have rapport with members of the health care team especially providers. I also don't know all the nurses super well, though I do ask questions, I feel like someone's impression of my can be made very quickly and possibly not give the whole picture of my ability. 
For example, I was having a really bad day, I wasn't feeling well, and it was a busy shift, but I was doing my job and I felt competent but tired. The nurse I handed off to wasn't super friendly and caught that I hadn't used the electrolyte protocol to replete afternoon labs, which for me was a super dumb mistake and also I partially blame their emr because the way it's formatted makes it so easy to miss certain orders. it wasn't critical but I felt bad missing it. I had extubated 2 patients so it was a little hectic. Then, I didn't ask the team about CIWA, but they also didn't address it or put orders in so I didn't address it, maybe I should have. my patient didn't show any signs of withdrawal. Lastly, this is very dumb, but I've had lots of heparin drips and never had to bolus. So stupidly, I looked at the tb syringe and was like how the heck do I push this as an IV. I was so tired I asked the RN coming on and she showed me the syringe to use. I felt sooooo dumb when I left that day, but also know my patients were safe. 
I've also had great days where ii've caught early cardiac surg complications and done everything to address them. I'm also remediating at home with knowledge I feel like I'm missing. I'm doing lecturly and ccrn classes to increase my knowledge. 

Also, the areas I'm most nervous about are codes and rsi's. It sounds crazy but I've never been in an actual cardiac code. It has just never happened to one of my patients. I've had airway issues mostly but never cardiac arrest, never seen the ACLS algorithm in real life. I had one RSI but someone else drew the meds and didn't show me. I really want to get hands on and use the meds because that is what I'm most nervous about doing in a quick situation. 
How do I know if this is not the right fit for me? is it okay to be a slower learner as long as I'm safe? 

Thanks!