Your hotel is just steps from the #8 tram line, which you can take to the Trastevere station to get the train to Civitavecchia.   The regional train isn't horribly crowded going toward Civitavecchia in mid-day, so if you're aiming to be at the cruise port between noon - 2 PM you should be fine.   The train from Civitavecchia is direct, but it makes a lot of stops along the way.  The fare is 4,60 euro.  For example, there's a train at 12:27 that arrives to Civitavecchia at 13: