I think that there is an unconnected place on the border of this circle.
I think the circle isn't quite complete somewhere.
ご質問ありがとうございます。
① "I think that"=「私は~と思う」
"there is an unconnected place"=「繋がれてない部分がある」
"on the border of this circle."=「この円の境界線上に。」
② "I think the circle isn't quite complete somewhere."=「この円はどこかで不完全だと思う。」
ご参考に。