Just like everybody already mentioned, they will want to see where the money came from.
A large deposit will be a BIG RED FLAG.
Few other options:
1- Deposit the money, wait 2 months before applying for mortgage? (so you don't have to show proof of where it came from)
2- Pay everything you can with the $3000 (utilities, gas, food, furniture, etc), saving more money in the bank?
Good Luck!
Starting Score: 700