This is a unusual situation. On one hand you knew that the rent was supposed to be $1145. What did you negotiate? If you really thought that the rent was supposed to be $995, and both you and the landlord signed, then you may be ok. The problem here is that if you knew, it would be a mutual mistake and the landlord could ask you to sign a new lease and pay the "correct" rent of $1145. But if you honestly thought that the rent was going to be $995 and they made the mistake, that is a mistake of the landlord only and they could be held to it.
The issue is if you truly knew.
The difference is $150 a month. That is quite a bit of money. Do you want to risk a fight with them and problems later. Maybe you can negotiate somewhere in the middle. The case turns on what you knew. But if you thought $995, then you can stick to your guns and hopefully stay at that rent until the lease expires. But don't expect any favors and if they might have been inclined to give you a break in the future, it definitely won't be happening now.
This is general legal advice intended for informational purposes only and does not create and attorney/client relationship. If you wish further advice, please contact an attorney of your own choosing or you may contact me for further advice and make other arrangements including retaining my services.
Generally speaking, the property manager cannot change the lease unless you all agree. They may also be held to the amount stated in the lease agreement.
However, a court might allow the greater amount if that is what you knew you were supposed to pay and agreed to pay, on the grounds that there is a mutual mistake in the contract.
I would try and work something out with the property management company. Maybe enter into a new lease with the correct amount, and their agreement to waive any amounts claimed from the earlier months.