He impressed in his 18 games and earned a permanent deal under boss John Ward, who previously managed the midfielder at the U's.
However, O'Toole admitted that when he signed for Rovers, he expected them to be challenging for promotion this term.
"When I joined I would have hoped to have been in a higher position than we are at the moment. I wouldn't have signed otherwise," he continued.
"It's been nice playing, but it's been frustrating as we haven't been doing that well. We've got a good squad here, I just think we're all under performing a little bit. We need to get up the table."
Ward realistic on O'Toole's stay
Six years ago, O'Toole was playing in the Championship with Watford, where he started his career, and scored 12 goals in 66 games across two seasons, and he believes he has what it takes to return to that level.
"No disrespect to League Two, but I don't want to play here. I want to play higher and do the best I can in my career. But it's not worth getting wound up about. I've just got to look after myself," he said.
"If it happens, then great. If not, I'm not bothered. No one owes me anything in football and I don't owe anyone anything. I just want to play as well as I can and do as well for the team as I can.
"But hopefully one day I'll play at that level again and I'm more than confident I can do it."
Bristol Rovers take on Burton on Friday night, looking for their first back-to-back league wins since August.
And despite being embroiled in a tight relegation battle in League Two, O'Toole added: "I'm not worried about getting relegated.
"If we get relegated, we should all hang up our boots. It just shouldn't happen."
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