I think I may have violated academic integrity last year - what should I do? I think I may be overthinking things, as I’m known to having a huge guilt complex.

As an undergraduate last year, we were given a coding assignment to complete that was worth 15% of our overall mark for the course. We often worked on it at computing practicals where students worked together in computer labs along with postgraduates who could assist you if needed. 

Towards the end of it, I had managed to complete the first two parts of it, but struggled with the final portion, and there were no more opportunities to ask for help at the practicals. 

Eventually, a friend of mine’s close friend (who I was still becoming closer with) figured out how to do it, and showed us a screenshot of his code. I initially copied it down so I can see what he did, and then spent some time reading it to understand how I was meant to go about answering it properly, and then tried to write up my answer knowing the right way to go about it, but it couldn’t be done in a way that didn’t look very similar to what my friend did. So I fear I copied. 

I didn’t think anything of it at the time, and submitted it, and it was marked and that was it. I think there may had been a plagiarism checker but I can’t remember.

Recently, I’ve since been worried that I’ve breached good academic practice. I don’t know why I’ve never thought about it much until now. 

As well, in a module I took last semester, I had worked together with friends on homework sheets that we handed in but people often completed in groups, which I think was perfectly permitted. I only worked in groups if I couldn’t solve anything, so there was a time last semester where I went to a friend who went over with me how to do the homework assignment (helping me through almost all of it) which allowed me to get a decent mark on it as I now knew how to do it with his help and instruction (they also were intentionally meant to help our understanding more than assess us apparently). I’ve also had trouble saying no to people who want to look at my homework for help, as I’m not very assertive. 

I’ve figured out that this could be poor academic practice as I’ve aided and gotten aid for assigned work recently. 

I just don’t want to think I’m an unworthy academic. What should I do? Should I contact someone? Should I just let it go? I’ve told myself for now on when asking for help from colleagues that I will never ask for answers but merely understanding, and to my knowledge I’ve not done anything else that’s improper other than this. 

Should I be ashamed of myself?

Is this situation a common thing, even among academics? I’m going to be at an internship over the summer with very esteemed academics. Am I likely different from them in my academic scruples given this described past behavior? Should I look down upon others who’ve done minor things like this who don’t feel guilty about it?
The past is the past and cannot be undone. Whether you are ashamed or not, you need to move on. But you don't need to invite external punishment for past misdeeds that haven't harmed others. 

It is best if you do your own work, of course, since that maximizes your learning. It is worst if you copy since you haven't really learned anything. In between is getting hints about things, with various graduations of that. The best hints come from your instructor, since s/he can give you a minimal hint to get you past a block so that you can advance. Getting hints from others is worse since those others may not be taking your educational development in to account. 

So, for the past, let it go. For the future think about the goals of the exercise, not just the end point. Seek appropriate assistance that won't hinder  your learning rather than inappropriate assistance that might. 

Probably you transgressed norms since you describe it yourself as copying. But treat it as a learning experience and move on.