Overpowered and unusual
This spell is pretty unique among cantrips, but that is likely a good thing as it makes it worth taking. However, the mechanics aren't quite right in this current version.
Fixed Spell Save DC
As a cantrip, this spell should use the caster's spell save DC rather than a fixed value. You don't need to specify the DC as part of the spell.
There are no official cantrips in the game that deal damage on a successful save. While spells typically have a successful save do half damage and negate side effects, successful saves against cantrips negate the effects entirely for that creature.
Area of Effect
Currently there are only a few cantrips with areas of effect: Sword Burst, Thunderclap, and Word of Radiance. Notably, all three share two features: a 5-foot radius centred on the caster, and 1d6 damage.
A 30-foot line is distinctly better than a 5-foot radius; it makes it a lot easier to line up multiple targets without putting yourself in danger or relying on them to be close to each other. This makes your cantrips stronger than any of the existing AoE cantrips.
Given the increased area of effect, I actually think 1d4 was a good choice here. It goes a long way toward making the spell more balance. One thing to remember, though, is that damage cantrips scale with level. Typically this would mean including a section like:
The spell's damage increases by 1d4 when you reach 5th level (2d4), 11th level (3d4), and 17th level (4d4).
Applying a Condition
Knocking a creature prone is a powerful benefit, particularly if you can do it right before your allied fighter's turn. There is currently only one cantrip that applies a conditions such as prone, though some others have additional one-time effects (such as Vicious Mockery, which imposes disadvantage on the target's next attack roll).
Sapping Sting, from the recently released Explorer's Guide to Wildemount, deals 1d4 necrotic damage and causes the target to fall prone on a failed Constitution saving throw. Importantly, it is a single-target effect, so yours is strictly better as it deals the same damage and effects but can target additional creatures.
I would suggest removing this effect entirely; it makes the spell much more in line with a leveled spell rather than a cantrip, and is therefore overpowered.
The current version of this spell is overpowered and has a few features that don't align with how cantrips usually work. When developing the next version, I suggest comparing your spell against other existing cantrips in the game.