In Britain we sometimes call that act 'bunking in'. Some examples I found:
"Meanwhile John Beggs QC, who represents police match commander David
Duckenfield, has previously suggested that Mr Dalglish once said that
10,000 Liverpool supporters bunked in to one football match."
"my uncle who'd bunked in to Wembley left at half time"
"The Odeon London Rd [cinema]... bunked in to see Oliver! a world
record 126 times"
"most of the parka clad kids I had bunked in to see 'Quadrophenia'
"But this is a slight film and even at an hour and a half it seems too
long. Good thing I bunked in to it and didn't pay. "
I expect 'sneaking in' might cover this in a more formal way as well. For the simple past tense, many, if not most, British English speakers would prefer 'sneaked' to 'snuck', which they might view as an Americanism, but these days one does see it, er, sneaking in to UK news reports, especially in the less formally inclined news media.
'Gatecrash' means to attend a specific event such as a party, wedding, etc, without having been invited, so would not fit this meaning.