I was caught
In the middle of a railroad track
I looked round
And I knew there was no turning back

The subject was in a difficult situation, Probably a youngster kicked out of his parents' house,(likely by his father) because of his behavior(party, no job, bad friends and for sure drugs). The argument was heated and he knew that after that there was no way back. He was on his own.

My mind raced
And I thought, what could I do?
And I knew
There was no help, no help from you
Sound of the drums
Beating in my heart

He was very scared to hit the road on his own
with no financial help from his father and nowhere to go. But that was it, after what was said there is no way he would beg.

The thunder of guns
Tore me apart

The memories of what his father said to him were
too much for him to handle, it was resounding in his head over and over(like gunshots), and that made him feel very sad.

Went down the highway
Broke the limit, we hit the town

He was not alone after all, a friend was there with him. They decided to take that opportunity to party harder and make a little trip.

Went through to Texas
Yeah, Texas, and we had some fun
We met some girls
Some dancers who gave a good time
Broke all the rules, played all the fools
Yeah-yeah, they, they, they blew our minds

The best memories that he can recall from that time were these dancers they met probably at a strip club.

I was shaking at the knees
Could I come again please?
Yeah, the ladies were too kind

They had a good time!

Yeah, it's alright
We're doing fine
Yeah, it's alright
We're doing fine, so fine

After all that he realized that there was no reason to be scared of going away from home.
It actually was a good thing.

In conclusion, the meaning of "Thunderstruck" is that line in time when things change so quickly that makes our heart race, and definitely leaves a deep mark in our life timeline.