Consider yourself exceedingly lucky that Macy's did not summon police which they habitually do where the amount taken is significantly less than the $150 that you stole. I doubt any agreement you signed forbids you from making online purchases or returns. As for the 3 year store ban, this is probably not as straightforward as the Macy's "no trespassing paper" might lead you to believe. Does it mean that if you walked into Macy's in 2.5 years and attempted to make a purchase, police could be summoned and you could be cited for misdemeanor trespassing for violating this agreement? There was a widely read 2003 NY Times article that reported on Macy's private jails and in-store investigative tactics including pressured confessions, racial profiling and in-store fine payments http://www.nytimes.com/2003/06/17/nyregion/in-stores-private-handcuffs-for-sticky-fingers.html This led the then NY State Attorney General to launch an investigation of Macy's tactics which were found to be illegal and led to a settlement of $600,000 which surely is just a small tax write off for this multi-billion dollar company. Notwithstanding any of this, you are well advised to avoid Macy's like the plague and not enter any of its stores for at least 3 years.
It matters on the wording of the agreement you signed, but in my experience with such promises, they apply to any Macy's (or other big-box retailer) anywhere, i.e. even in another county or state. Macy's does not want to see you again, even in another state or county. I would look closely at the document. It probably says "in any place" or something similar such as "under any circumstances."