Jackson Arnold got a bit of a baptism by fire for his first college start, stepping in for his Oklahoma squad in the Alamo Bowl against Arizona last winter. But through the challenge, Arnold learned plenty. Arnold had an up-and-down day, going 26-of-45 for 361 yards and a pair of touchdowns, but he tossed a trio of interceptions in a loss. Even still, the experience was a valuable one for Arnold, who is now the full-time starter in Norman. “It’s tough,” Arnold said of the situation. “You don’t want your first college start to really be in a bowl game against a good Arizona team, but for me I j…