No, First Strike doesn’t trigger your creature to deal injury twice; it solely causes your creature to deal injury earlier than regular injury is dealt.

702.7b If not less than one attacking or blocking creature has first strike or double strike (see rule 702.4) because the fight injury step begins, the one creatures that assign fight injury in that step are these with first strike or double strike. After that step, as an alternative of continuing to the tip of fight step, the section will get a second fight injury step. The solely creatures that assign fight injury in that step are the remaining attackers and blockers that had neither first strike nor double strike as the primary fight injury step started, in addition to the remaining attackers and blockers that at the moment have double strike. After that step, the section proceeds to the tip of fight step.

So within the second / common fight injury step, creatures with first strike won’t deal injury, as a result of they already dealt their injury.

If your attacking creature is blocked by a 3/1 with first strike, it might take a complete of three injury. If it has 3 or much less toughness, then it should die within the first strike injury step, earlier than it could deal injury. If it has 4 or extra toughness (which Goblin Machinist does), then it should nonetheless be alive to deal its injury after it has taken the three injury.

Your pal could have been complicated First Strike with Double Strike, which is a capability that causes creatures to deal injury twice.