A fear of heights is not uncommon (or unreasonable). The climb is about 70 feet, which seems like a lot, but consider 20 yards on a football field... doesn't seem THAT high anymore.
Also, it's not straight up. True, going higher will feel steeper (and going to the very top DOES feel high), but for "up and over" it's less steep. So don't think of it as climbing a wall. You're basically climbing a big, tight cargo net. It's solid.
Later you're allowed to climb as high as you're comfortable with.
If you're afraid of heights it's fine to let someone there know. You're not going to be the only person afraid of being high up or falling, so don't be worried about being "different."
If this is the scariest, most uncomfortable thing you do all summer, consider yourself lucky.
You'll be fine. And this will be the first self-imposed barrier you break down during a four year span of breaking down self-imposed barriers!