I understand that you want to be polite, but using polite language between friends is on the contrary rather strange.
Being polite is great, but using polite language with your friends is on the contrary kind of strange.
この分の「逆に」は「on the contrary」です。
「変」は「strange」といいます。
例えば、日本語を勉強している留学生に教えているなら、下のような文になります。
I understand that you want to be polite, but using polite language between friends is on the contrary rather strange.
丁寧でいたいのはわかるが、友達同士で敬語を使うのは逆に変。
Being polite is great, but using polite language with your friends is on the contrary kind of strange.
丁寧なのはいいけど、友達同士で敬語を使うのは逆に変。
「敬語」は「polite language」また「honorific language」でも大丈夫です。