Unexpectedly
More Than Expected
Something that happens outside the plan is something that happens unexpectedly.
あんがい
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
日本語学習は私にはかなりハードルが高いんじゃないかと思っていたんですが、案外そうでもなかったです。
I thought learning Japanese would be very difficult for me, but unexpectedly, it actually wasn’t that bad.