I think you are thinking that size matters more than it really does. I'm 5'10 and weight 82 kg and I made it to the all-stars team of my collegiate conference. If you keep working on skills and get experience and practice your heart out, the coaches will notice it and believe me, they do take it into account. And do try for wing position first as it is a very good position to start. And you have a good height so don't be so worried.
Size has little relevance in Rugby it's more about strength, skill and attitude as I'm a prop 68kg 5ft 11 and I can win a scrum with ease. But the main part of rugby is attitude most people should tell you that as if you go in ready to put your body on the line you come out with pretty much no injuries with if you go in 50% you actually come out with loads it's strange but it's rugby. Goodluck with your rugby career and never judge people on their size it's the biggest mistake you can do in rugby
You're size honestly doesn't matter. All that matters is good technique and a healthy diet never hurt anyone.
you don't have to be big as long as your fast to run down the wing try a position like on the wings or fullback.