Playtesting "Adventure Path"

I've spent the last few weeks writing up a new solo RPG which takes inspiration from "Four Against Darkness" and the digital card game "Slay the Spire". With the first draft of the rules complete it was time to do my first playtest. The following are my notes from the far too short game.

My characters

• Soldier Hp(14) Melee Attack +1 Melee Defence +1
• Bandit Hp(10)  Melee Attack +1 Initiative +1
• Elementalist Hp(8)  Danger Sense +1 Earth Shield +1
• Acrobat Hp(9)  Dexterity +1 Initiative +1

So with my party ready to go, I started my first move up the map. I had a choice of overland or underground encounter, I opted for the slightly easier overland encounter.

Move 1 -----

Move to Helmet Encounter, Difficulty mod +0

Encounter (4) Constrictor, attacks character with most hit points

• HP (12) Melee Attack+2 Damage Bonus +1, no treasure

I rolled initiative for characters and monster.  Monster rolled a 1.

Acrobat melee attack +0 > 4, Constrictor reduced HP to 8

Soldier melee attack +1 > 3, Constrictor reduced HP to 5

Bandit Melee attach +1 > 6, Constrictor reduced to 0 HP

A win for my heroes, but alas the constrictor has no treasure.

Move 2 -----

Move to Helmet Encounter, Difficulty mod +1

Encounter (10+1) Wererats # App (1d4+1) 5 ,Melee Attack +2, Melee Defence +1 8HP each.

~Round 1~

WR1 Hits Soldier doing 4HP damage

WR4 Hits Bandit doing 3HP damage

Acrobat hit WR1 doing 1HP damage

WR5 Hits Elementalist doing 6HP damage

Soldier Hits WR1 doing 4HP damage 

WR3 its Acrobat doing 8HP damage

Bandit Hits WR1 doing 4HP damage

Elementalist Hits WR2 doing 6HP damage

WR2 Hits attacks soldier doing 5HP

~Round 2~

Soldier Hits WR2 doing 5HP damage

Elementalist casts "Earth Shield"

WR4 Hits Bandit Doing 1HP of Damage

Bandit Hits WR3 doing 4HP damage

Acrobat Hits WR3 doing 5HP damage

WR5 Hits Bandit doing 1HP damage

~Round 3~

Bandit attacks WR4 doing 5HP damage

Acrobat attacks WR4 doing 1HP damage

WR4 attacks Acrobat killing him

WR5 attacks Elementalist killing him

Soldier attacks WR4 doing 2HP damage

~Round 4~

Soldier attacks WR5 doing 3HP damage

Bandit attacks WR4 doing doing 3HP damage

WR5 attacks soldier killing him

~Round 5~

WR5 attacks Bandit killing him.

... and so ended my party of adventurers. I expect the game to be swingy because it does use random die rolls to determine encounters. I even think it was back luck to roll 10+1 on the second encounter (were rats) and then to roll the maximum number of enemies 1D4+1 (5). My first inclination is to "harden" the characters, perhaps by giving them armour/shield to act as damage reduction. However I'm not sure if one single play test attempt is a good place to make changes. After all, solo games have to have extreme challenge.

Edit, I'm definitely going to make another playtest before changing anything.