Ok - actually the Drummer and the bassman are the two most important dudes in a band for they are the backbone. if they are realy good and glued to eacother (in terms of accuracy and groove) then you´ll have an easy life as a guitarist. Theres nothing to be afraid of when joining a band. i dont think that its a mega-famous band, is it? so if you are making some mistakes (and you will make them - aswell as every other dude in the band will), then so be it - as long as you dont stop playing everytime you miss a note, its ok!