how do I get my bitcoin back into my wallet?

Once you send them to someone else, they are no longer your Bitcoin so far as the Bitcoin blockchain is concerned.

Bitcoin transactions cannot be reversed

Since Bitcoin transactions are irreversible, the only way to get your Bitcoins back is to contact the exchange, business or person you paid them to and ask them to create a new transaction to reimburse you.

It may be worthwhile first checking their terms of use to see how they handle this situation. They may have a policy of not getting involved in sorting out this kind of mistake involving small amounts - or they may charge you for their staff costs in sorting out your mistake.

Excash

If by "Excash" you mean some kind of in-game currency used in a multiplayer online game, you may need to contact the business that runs the game and ask for their help.

If by "Excash" you mean www.ex.cash run by "Zebiex". They don't seem at all trustworthy to me. Minimal website, recently set up in the last few months. I can't imagine why anyone would send money to such an apparently sketchy business.

There are a lot of websites using similar names (e.g. exkash) but I doubt I'd find any of them to be trustworthy.