should be fine…
i’ve used bikes with a triple shifter and mech with a double chainset, with no ill effects. what are the problems you’re having exactly?
my workflow would probably be:
1) fit the chainset and the mech but not the gear cable
2) adjust the inner limit screw until the chain runs freely through the mech on the inner ring
3) fit the cable with the lever set to 1, pull hand tight and secure
4) push the lever from 1 to 2 and back and check the shifting. sometimes you need to slightly adjust the angle of the mech to get the best upshift/downshift, or take up slack in the cable
5) try pushing the lever from 2 to 3: the chain may fall off the the outside of the big ring if so, adjust the outer limit screw
or something like that 🙂