Well its the company's responsibility to give you training so maybe talk to the CEO or the head of company

Maybe you can find another company or demand a raise. You could also try to hire another more experienced person to help you

Being the only one, you would be considered the head of structural engineering, correct? So request a meeting with the heads of your company and talk about hiring some new recruits, or at least sending you to a proper training.

I imagine your degree knowledge will kick in soon enough, in the meantime talk to your boss's boss and ask about hiring a replacement for him, explaining that you're inexperienced, and if you and your old boss had a good relationship perhaps contact him and ask for advice?

Only one way to gain experience! Jump in the deep end! But Good luck op I'm sure your training will get you through, if you get overloaded maybe look to find a mentor in the industry that can give you advice.

Talk about "trial by fire".. honestly I'd think of this as an opportunity to show people what your made of! Good luck OP

there's no shame to ask for help, naube your college professors?

You would be surprised how informative Google is; when I was a software dev apprentice I used it all the time. For all the cruelty on the Internet the community can be really helpful sometimes

On the upside, think about how good you'll look to the higher-ups if you can pull it off.

On the upside this means that you have the chance to be the new boss of that company just work at it and I'm sure that you will achieve