Missed job opportunity

Why didn't you accept the job that you had experience in, that paid more and was more interesting? I'm asking because it will be a good indicator as to whether this was a genuine error or you're just a flake because this is what the first company is going to be thinking and will be the deciding factor whether they are prepared to give you a second chance.

I didn't have experience in either role - the job I did over the summer was completely different. My current role and the second one I was offered are similar, but now that I've experienced the industry and have a better understanding of the different job roles, the initial one I was offered interests me more. At the moment I just do admin, but during my training I was introduced to other roles within the company which I found to be way more interesting, and parts of these roles were exactly the same as the first offer. This is why I'm kicking myself slightly.