"Pattern" is something one does with a shotgun. "Group" is the term you're looking for here.

But it's not as simple as "here's my equipment, what do I need to do". Were you shooting from a benchrest, sandbags, prone unsupported, .....? What's your experience level? There are a LOT of influences that may or may not tighten your groups up. But, seven inches at 350 does bear that something's probably not quite optimum here.

One doesn't just pick up a rifle and become a 1 MOA shooter at 350 yards.