I'm assuming you were qualified enough for those positions if they came through a school board. Any idea what the competition was? Could you reach out to those companies again and ask for some feedback? If you've sent so many applications and got no response at all I could see 3 potential problems - there is a major power outage, the local market is ridiculously crowded (maybe plain crap) or there is something wrong with your application that doesn't even get you a screening call.
Apart from the above, and with all the great advice from other posters, I'd suggest to create a LinkedIn profile and start building a network asap for a bit more of an outbound personal marketing.
Don't only connect with people who work in hiring but also with other more senior software engineers - they usually have established networks that you will be able to access if you post anything. Ask a couple of them if you could get a review of your CV / some advice on the market, you might learn a lot from them. While not everyone will agree to your request, you'd be surprised how helpful and kind strangers are.
Once you think your network and CV is sufficient, drop a post saying what you do and what kind of work are you looking for. Then reach out to those connections you added previously and ask if they could hit 'Like for more exposure' - this will bump up your posting in feeds of their networks. Adding this method to my past job hunts has been an awesome boost and got me great gigs that I wouldn't even know existed, pretty simple yet effective.
> I'm afraid because I haven't bothered to work on mastering any of them
Try at least one - it's not a waste of time even if you end up using something else on the job. I'd pick something popular (javascript and friends maybe) to increase your chances of getting through the first interviews.
> employer wouldn't wanna take the risk on me being able to learn their stack.
That is probably slightly true but in my opinion the point of an internship is to learn. I wouldn't hire an intern and expect them to be experts. Technology changes very often and even senior engineers have to learn new stuff on the job too. Very rarely people who just graduated have all the knowledge and know the exact stack in and out. Don't let this slow down your efforts.
Good luck!