One thing to keep in mind - some orgs just have more challenging projects so keep looking, it may take you looking into 10 or 12 orgs before you find one that seems like it's a better fit with your skillset. Many orgs have mostly 'easy' projects which really are geared toward someone who is excited to learn but has basic coding experience in a particular programming language or two.
It's totally normal to think you may not have the skills needed to do a particular project, GSoC is a program to help people who want to learn more throughout their GSoC experience and it's a platform for curious and excited developers to excel.
Of course you do need to be relatively comfortable coding in the programming language(s) used by the particular project since you will spend 3+ months coding on the project. In the talks we give we often tell folks if you have been learning coding for a year or more then you should be fine and can handle many of the projects in GSOC. Some projects are going to require folks who likely have been coding for a few years or more or have experience in multiple programming languages.
The main takeaway is there are a lot of different types of projects and mentoring orgs, some have more complicated codebases than others. You may want to stick to one of the easier codebases if you are feeling unsure of your abilities.
In some orgs, their project descriptions are definitely more complicated than others - that doesn't mean the project itself is complicated, just the mentor who wrote the description didn't make it simple for someone new to open source or their project to be able to understand the project idea.
To decide if you are 'technically sound' the best way to do that is to reach out to the org and talk with them. You'll be able to figure out very quickly if it's a good fit for your skills.
Best,