Celtic have drawn against Ajax and Fenerbahce in the Europa League so far this season.
The Bhoys have taken the lead against Ajax and Fenerbahce in Europe this season, but they have only been able to claim a point in both matches.
And Armstrong admits that they have been frustrated by their failure to win more regularly, with a match against Molde next on their schedule on Thursday night.
“We might have felt hard-done-by in not picking up all six points available, but we are still in a good position and if we take three points off them over there and then at home then the group will open up for us," the midfielder said.
Armstrong has played just a minute of Celtic's Europa League campaign so far, with injury halting his progress this season.
The 23-year-old was in excellent form last season, as he forced his way into the Bhoys' starting line-up after joining in January, but he now faces a fight to win his place in the line-up back now he is back to full fitness.
If Armstrong does appear against Molde on Thursday night, then it will be imperative that he plays well, as Celtic need to win the fixture.
Ronny Deila has made no secret of his desire to have a lengthy run in the competition this season, and his side will need to pick up three points against their Norwegian opponents if they are to stand a good chance of making it out of the group.