As it turns out you could be a great asset to a female rugby team. Starting out on the wing would probably suit you best as you aren't doing much of the physical 'grunt' work. I think your speed and agility will be great for beating defenders out wide. Especially if you are able to develop a good step and fend. Sure you might get a few knocks, but who doesn't? If you give it try, I'm sure you'll enjoy it!
Go for it! You will be fine, even if you aren't big enough to play in the team matches this year you will learn the necessary skills to be an excellent player next year. Obviously being bigger and stronger is an advantage, but you don't necessarily have to be massive, and personally i'd prefer to have on my team someone small and aggressive than a fat lump who cannot run.
Go for it. The worst that happens is you get knocked around a bit.
