7.0 is a neutral pH.

6.5-6.8 is pretty ideal for pH of the soil. And definitely add a little more soil to the cup, the stem will root itself under the fresh soil and will also strengthen it up a little. It looks to have stretched some. If air can't circulate at the base of the stem, things become stagnant, and I think the seedling is more at risk of developing pythium wilt.