This post has appeared on two other websites where I posted the following response:
Likely not without financial consequences.
The landlord doesn't have to sign it for it to be binding on you.
I don't know what kind of business you have or how long you have been in business but you made some rank amateur mistakes.
You should have insisted on both of you signing duplicates of the lease at the same time.
You should have insisted on the estimate before signing anything.
And you should have had a cap on the improvement cost and scope put in the lease.
I could probably come up with a few more if I sat here and thought about it long enough but I think that's enough for now.
Do you even have a copy of the lease or did you just sign one copy and hand it back without keeping one. If you didn't keep a copy that would be mistake number 4.
If you did keep a copy, take it to a lawyer and review your options.