No.
Daydreaming is either venial or not sinful at all, depending on the circumstances. Deliberately allowing your mind to wander because you don’t take the Holy Mass seriously, or view it as a chore, would constitute a much larger problem, but that isn’t what you are describing here.
Each time a person redirects themselves after their mind wanders, it is pleasing and meritorious to God.
Having something to focus on can help reign in a wandering mind, such as the candle next to the tabernacle, or one of the many pieces of sacred art in the sanctuary, along with focusing on your breathing and collecting yourself before Mass. If different thoughts are troubling or concerning you, you might say, “Jesus, I place all of my [fears, thoughts, distractions] before the foot of your Altar. Let your will be done in my life. I love you.” Mental spontaneous prayers can be repeated as often as is necessary. St Mother Teresa often did “blitz Rosaries” where she said a much shorter prayer on each of the beads and went through them very quickly.