I'd second Don's comments. I mostly play classical guitar, rather than anything else. *IF* (& I stress 'if') the injury is purely from guitar playing, it's not RSI on that little amount of time. It's bad technique, pure & simple.

I'd only differ in suggesting you find yourself a properly trained classical guitar teacher & take a few lessons to get your technique checked out. Despite the extra expense, it would probably be more cost effective than an non-interactive video that can't look at what you're *actually* doing & talk back!