A magnetized watch will run a lot more faster than that. anywhere from +1 min to +5 min a day. Also, I've been reading a lot about magnetism-phobia among watch lovers, but in reality, it takes a lot to magnetized it, like very close proximity to a speaker or a transformer.
In many cases, a watch caliber is calibrated before being cased to whatever factory setting the manufacturer has set. After which, it will being packaged, checked and transported and subject to whatever conditions before reaching the hands of the user. Don't be too alarmed if it is not running as per manufacturer specs, and yes, that's what warranty is for.
+7 secs a day is pretty normal and only requires regulation and should be a simple fix. It's really up to you but IMO, it's a minor issue and probably best to see if it may develop other problems along the way during the warranty period and sent it in for a more thorough service.