Is this a scam

I got a text after posting a couple pictures to my instagram page. Asking if I could take sport pictures for some seniors at a high school. They kept texting and eventually emailed me a check to scan for payment. However the email came from a completely different name and the check was already signed on the back. They also asked if they could include more because the videographer they hired is not able to take checks, as well as an extra $50 for “being helpful”. I only asked for $100 for the whole deal and they sent $1000. How do I go about this? If it’s real I don’t wanna be the ass and tell them no, but I’m also not trying to cash a fraudulent check.