I have used 93 octane - mostly ethanol free for 30,000 miles on my Roush 427 SR engine. It has had a tank or two of 91 octane and I am sure some of the time some ethanol (10%) has been added in, but when I check it, it has always been alcohol free.
If you are close to sea level and even up to 1500 feet or so elevation and the temperatures are cool - below 90, good 91 octane will run ok in the 10.5 : 1 compression ratio SR engine with the aluminum AFR heads if the timing is set at the recommended 31 to 34 degree total.
Bunch of ifs there so if you can run the 93 and don't worry.
BTW....if it were mine, I would drain out what you have in the tank and refill.
