The 25-year-old striker failed to convert the one clear-cut opportunity that the Sulphurites managed to create during what was an underwhelming performance at Wetherby Road on Saturday afternoon.
The game would eventually end goalless, but with 44 minutes on the clock, Ryan Fallowfield got forward from full-back and delivered an inviting low cross from wide on the right, picking out Armstrong at the near post.
The in-form ex-Middlesbrough attacker was however unable to apply a finishing touch from close range, diverting the ball across the face of goal and wide.
“I’ve ended up going too far past the front post, so I’ve had to get a little touch on the cross rather than a good contact and I just didn’t quite get enough on the ball, which is really frustrating,” said Armstrong, who has netted six goals in nine games since joining Harrogate from Salford City this summer.
“It’s 100 per cent a different game going in at half-time if we’ve got a lead, it kind of wrecks their game-plan. They’ve not got anything to hold on to anymore and we can go on and probably get a few more goals after that.
“I am disappointed, but the main thing is that I’m getting in there and getting chances and more often than not, that one goes in.”
Harrogate Town: Oxley; Fallowfield, McArdle (Sheron 46), Hall, Burrell; Thomson (Power 66), Falkingham, Pattison, Diamond; Armstrong, Muldoon (Orsi 69). Unused substitutes: Cracknell, Martin, Kerry.
Stevenage: Anang; Wildin, Vancooten, Cuthbert, Coker; Osborne, Reeves, Taylor, Barry; List (Norris 77), Reid (Andrade 85). Unused substitutes: Bastien, Prosser, Smith, Marshall, Townsend-West.
Referee: C Boyeson (East Yorks).