I need help with the two underlined sentences 🙏🏻

1. Why is it 置いといてください　why is there a と instead of maybe just 置いてください　

2. Why is it押してありませんでしたよ　- specifically, てありません　instead of maybe just押しませんでした to say that he didn’t affix the stamp?

Thank you in advance for any explanations 🙏🏻

This is from the みんなの日本語textbook.