Not at all. I've done it all the time, even tho you'd think that with a seventh pregnancy I'd have it down by now! The window is sealed, so as long as you get enough on the absorbent end, your good to go.
Oh, I think I forgot to mention: with the 7 pregnancies that makes at least 15 tests that I have taken, plus additional ones where I thought I was when I wasn't....so way too many to count over my past 9 years of child-bearing.
Even if I splashed on the window, the test has always worked. And I have never had an inaccurate result. So don't worry about yours