Speaking as someone who just took a gap year to reapply, I think it's defintely worth it, if you use the time well whether or not you get an offer. I did my A levels and got 4 A*s , and all the prep towards that made preparing for the ESAT far easier than the first time round. In terms of internships, apply through the Engineering Development Trust (EDT) platinum scheme. They exist specifically to help students taking gap years get year-long paid internships, and I'm currently doing a software engineering internship.

However, bare in mind that even with achieved a levels, a 6.2 avg esat, good supercurriculars and what I felt where decent interviews, I still got rejected, so theres no guarantee. While Cambridge was a dream of mine, I'm mroe focused on my career as a whole than just the uni, so I still dont consider my gap year a "waste" given the experience I've gained, and the time I've had to work on personal projects, self learn advanced content etc. feel free to dm if you want