You should be fine then - the other reason the ! appears is sometimes when there is too much text in the text box and there's a risk it won't print. It can be worth re-doing the page template to see if making the picture smaller will stop the ! appearing.
It is worthwhile upping the resolution using Prefsetter - printing at 300 rather than 150 does make a difference - and it will take you 5 minutes to download and make the change.
Before Christmas? You should get it back in time. I sent one off last night which I want for Christmas. It was suggesting shipping in 3-4 days (last time, it shipped in 2 days despite saying that).
It's the length of time in the post though that seems to vary, particularly at this time of year. In the UK, they come from Germany so I have my fingers crossed that it makes it in time for Christmas; I've posted it to the address where I'll be rather than my home one to give it an extra few days. Last time I ordered (in June), I ordered on a Sunday night and it was delivered a week on Tuesday (so 9 days but 7 of those were in the post!)