Why don't you just give the trials ago.. chances are you aren't going to be the worst their, you just don't have big enough confidence. Just go for it.. whats the worst that's going to happen? You may be able to learn from the trials and get more involved in rugby! Give it a go! good luck.
if u have been asked to go then your coach must think u are good I know how u feel u don't think u are good but u really are im 15 the same size as u 5'2 and play flank on my high school sr girls team I have a good tackle and a good catch and pass I am an average speed for a back and a fast forward so just go to the trials if u don't want to play with that team then just go for the experiance
It won't kill you to have a crack at it. You will get excellent coaching if you get into a team. All rugby is fun.