Rest Day- My favorite day!

At long last, tomorrow's my last shift at work and it this only means one thing, relaxation time. I'm going to spend my two days off with my family and of course watching movies.

Hi! This is really good, but there are a few things to note

'At long last' as an idiom, really only works with something that has already occured, or is happening in the immediate future. So you could say 'At long last, i have finished my final shift at work and...'

I would say 'this' instead of 'it' because the thing that creates the meaning (your final shift) is  mentioned in the sentence. :). I am also not sure you can say it means only one thing in this context, I think it is too absolute for this kind of statement. Perhaps 'there is only one thing on my mind' or 'this means only one thing to me' - this allows other meanings to exist, but it says that only one matters to you, in this moment.

Last thing, the final part of the second sentence does not fit perfectly. This is because of the location of your verbs & conjuctions. Here is what I would say: 'I am going to spend two days hanging[verb] with my family and [conjuction] of course, watching [verb] movies'. When you use 'and' to link activities like this, it is expected that there will be two linked verbs. The way you have written it, would be the same as 'I am going to tagaytay, and of course, watching movies'. Hope this helps!