I used to feel this way too (knowing about a broad range of things, but thinking I was not good enough at anything specific to be "hireable"), but luckily I realised this is not necessarily bad. Generalists are ideal people to found a startup and they can be a huge asset to have at any company, especially at small companies / startups. And furthermore, don't push yourself too hard, at the end you're still a student. You can specialise later if you want.
