As you can tell from her photograph, actress Nell Barlow exudes Big Mary Elizabeth Winstead energy in “Sweetheart,” a light British rom-com about coming of age when you’re gay, confused and in your teens.

It’s a pity her character April, or “AJ” as she’s now billing herself, can’t see that. That’d be a great confidence booster for someone at her age, when self-loathing is our default setting.

AJ is the caustic, hyper-critical narrator of her summer vacation/summer romance story, a reluctant hostage to her mother’s “caravan resort” (RV trailer rentals) family holiday somewhere near Bridport, Dorset, another piece of Britain’s White Cliffs coast.

That not-quite-incessant narration is a rare misstep in writer-director Marley Morrison’s sympathetic comedy about being at that “experimenting” age in life, something parents have even more trouble with than their confused, fumbling-about-in-the-dark kids. AJ is at her most quotable when speaking aloud, often arguing with her Mum (Jo Hartley).

“Why can’t I just do what I want?”

“Because it CHANGES every five minutes, April!”

To her credit, her mother is supportive of her middle daughter, even if she’s seeing a long list of passions, phobias and dreams that all look like “phases” to her. April abruptly decides to become “AJ.” April’s chopped off her own hair, which better suits her shapeless, fashion-free wardrobe. April wants to quit school, not go back for her senior year (she’s 17).

“AJ” plans to go to Indonesia to volunteer to “knit jumpers for elephants,” who are “freezing to death” due to climate change.

The dear. It’s no wonder so many parents are dismayed when we hit our middle to late teens. We’re all head cases.

But this trip to the caravan resort will be her chance to “switch off” her phone and her head for a few days. The family has long come here, although this year, Dad’s “not invited,” and maybe never will be again.

What Mum really needs is April’s baby-sitting help with her eight-year old sister, Dayna. What Mum really wants is bonding time with her oldest, 29 year-old Lucy (Sophia Di Martino), who is very pregnant, with laid-back boyfriend Steve (Samuel Anderson) in tow.

What AJ needs, she quickly figures out, is a girlfriend. But even if lifeguard Isla (Ella-Rae Smith) is a sexy combination of Scary Spice and Sporty Spice, even if she’s quick with a friendly smile, “Girls like her like boys.” Or so AJ believes.

Most every plot point, character and situation in Morrison’s debut feature is borrowed from earlier romances, or is at least so familiar as to be rom-com — gay-or-otherwise — comfort food.

The resort has a Catskills “Dirty Dancing” touch or two, with the staff carrying on affairs with each other, and with guests, and nightly entertainment a part of your holiday package. Phil the Magician is one of those entertainers. He introduces his assistant, “Bendy Wendy,” a “contortionist” just “trying to make ends meet.” Yes, there’ll always be an England.

The stages in AJ’s shy, insecure love connection to Isla hit the same sorts of roadblocks such romances always do in the movies, with one or two of them playing as particularly contrived here.

But the cast is spot-on, top to bottom, and the leads are engaging and romantic except for when they’re being teen and mean.

They make sure we buy in on whatever they have going on, and that we’ll keep an eye out for Ms. Barlow and Ms. Smith and wish them just as much luck in their future endeavors as they have as each other’s “Sweetheart.”

Rating: unrated, teen drinking and drug abuse, sexual situations,, smoking and profanity

Cast: Nell Barlow, Jo Hartley, Sophia Di Martino, Samuel Anderson and Ella-Rae Smith,

Credits: Scripted and directed by Marley Morrison. A Film Movement release.

Running time: 1:43