First live gig soon

I have my first gig soon with my band and we're thinking of covering Do Me A Favour (we only have time for one song since it's multiple bands, school orchestra, choir, carol choir, etc). I'm on rhythm guitar (grade 4) and lead vocals. I'm a confident guitarist but I want to know if it's the right song to leave a mark on the audience so they go away and remember us. Is it the right song to do? If not, what do you guys think we should do instead (preferably something impressive but not too difficult)? Concert in 3 weeks so we have time to rehurse different songs.