Contact your bank immediately. Explain to them that you suspect you've been targeted by a fraud. Do not spend that money! When/if that check bounces, you will be held liable.
If you are contacted again by the sender, try to amass as much info. on them as possible. Do not forward, in any way, any funds to them. File a police report as soon as it becomes obvious that this is a fraud. Which will be quite soon.
Be safe. Be aware.
Gunnar