The Scottish outfit completed the double over their French rivals with a 21-10 triumph at an icy Scotstoun and boosted their chances of qualifying for European the quarter-finals for the first time.
DTH van der Merwe scored a hat-trick of tries but the Warriors missed a string of opportunities to secure a valuable bonus point by adding a fourth.
And those misses could prove costly ahead of a final-round showdown with Bath at the Rec next weekend.
"It was frustrating to spurn so many chances to score tries," said Townsend.
"I think when you go up against a French team and win you should be really happy - and we've now done the double over them - but as you can tell we are disappointed by how we didn't make the most of our opportunities.
"Maybe it was over eagerness, or our accuracy or decision-making in that last 22, but it wasn't at the level it needed to be today to get the victory that we wanted.
"When you create so many opportunities and put pace on the ball and get down into their half, then it's about outworking the opposition and tries or penalties will come.
"But we maybe rushed things too much and didn't get in our right shape and that proved costly."
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