Hagámoslo..........
This appears to mean "We did it!" but why subjunctive here, seems like a definite action.
4 Answers
I think it means "Let's do it!" rather than "We did it" though I wouldn't argue with you if you said you'd seen it used that way. I know it as the nosotros command form for hacer (with lo at the end.)
The correct spelling is "hagámoslo" (let us do it!)
P.D. The subjunctive is also used for "definite" things. The rule you are following is probably flawed.
delete-already answered
Oh man that makes more sense. Hacemos - we do it. Hagamos - Let's do it. I know this already my brain must have frozen up.......... ![]()