Did I give him the wrong impression?

Very good questions you pose....
I would tell you what I think---if a girl did the same thing you did, to me that is like giving me the green light to go to places that are beyond tickling and holding. Now, I'm kind of the late bloomer. Most likely when I was a senior I wouldn't have done anything. However, depending on how experienced guys are, they could have taken that to the next level.

The good news is that given the behavior this guy showed when in your room, it does appear he is really one of those nice guys out there, so maybe all you have to do is go with the flow and see how he responds next time. Let's assume he is a nice guy that had no intentions of doing anything sexual---if you bring it up that you made a mistake bringing to your room and sitting on the bed like you did, then maybe he will get offended and think, 'hell, I wasn't thinking of doing anything to you..I'm not like that...' And as you can see, you that wouldn't be a cool thing to do...

If he brings up the subject of hanging out in his room or in your room, then you can say, "well, maybe is too soon to do that again, I want to take things slowly." And if he were to say, 'but last time we hung out in your room, blah blah blah...' then you can say, 'well my mom had people over, but normally we would have stayed downstairs---consider yourself privileged." So as you can see, you're playing it cool, while at the same time letting him know you're not 'that type of girl'. :)
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However, from now on, you should be more thoughtful about what guys you bring to your room... :) As your friend says, you could give guys the wrong idea by this type of action.

You can still take things slowly. I've always ended up with guys in my room at some point in the relationship or another. It's where I'm me - even when I have a common living area that's usable (the one I have right now isn't, really - the roommate that uses it compulsively isn't the cleanest ever...), my room is still where I gravitate to.

I've also done the age gap thing - I dated a senior when I was a freshman in high school, and then again in college. In both cases, the guys were really patient with not going faster than I wanted to. One of the most important things in any relationship ever is communication (I've failed at this in almost all of mine, but I'm working on it). Tell him that you're not comfortable moving fast. If he starts heading somewhere you're not comfortable, stop him. You can ask him to stop, or simply stop the movement of his hand or whatever. If he *is* a nice guy (and it sounds like he is, since he didn't take advantage of the situation), he'll respect that and let things move at your pace.

However, if it makes you uncomfortable, don't use your room. Find somewhere else (when necessary) where you can be comfortable. While I was living with my parents, there was always a strict open door policy - if I was in a room with a guy, the door had to be open. Now, I pushed this many times, but the door was always open (even if my parents weren't home) and there was the constant paranoia of discovery to keep things slow.

And last, DO NOT be ashamed of not wanting to have sex. I shouldn't have lost my virginity when I did (in college, I decided I didn't want to be a virgin, so I had sex with my boyfriend), and it's much better to wait until it feels right for you.

Good luck!