accepting/turning down a position

I am currently employed at BOFA/ML. I was repositioned from an FADP role to Paycheck protection program. We were let know the position would be ending last month and given until 4/7 to find a job within the bank or be let go. I interviewed for an FSA position and they fast-tracked the interview process and offered me the job this morning. When i asked how long i have to accept the position, they told me i have to accept immediately and that i should have been thinking about this prior to receiving the offer. I have been in the interview process for a position i really want since January. would it be wrong to accept this position ( i know i don't want) and if the other company comes back and offers me a position( i do want) to just tell BOFA I dont want to accept the position? I don't know how to proceed, but they told me i have until 8am tomorrow morning to respond.