First off, is it bubbling yet?
I've used White Labs Sweet Mead yeast a few times. I don't recall having any fermentation issues. I believe White Labs claims a tolerance of 15% ABV, so I wouldn't expect it to be overly sweet. We just distributed a club mead project (100+ gallons) using White Labs Sweet Mead yeast. The OG was 1.112 and the FG was 1.000. I didn't expect the FG to be that low. We had aged the mead for a year in Lairds Applejack barrels. The Applejack that leeched out of the wood may have lowered the FG a bit.