Changing Color

I am new to this list, but need help! I am knitting a baby sweater with Heaven yarn. The pattern is stockinette stitch knit in pink with a white heart in the center of the front. I knitted most of the front, but where I carried the white yarn behind the pink, the sweater was puckered. I realized that I shouldn’t be carrying the white yarn behind so many stitches, but I don’t know what to do. I am knitting on size 11 with bulky yarn. I read the instructions on intarsia knitting, but I am only using 2 colors… and the heart is only for about 20 rows. The heart begins with only going behind 2 stitches, but at the end, I am going behind over 16 stitches. Can anybody tell me how to carry this yarn behind without having such a long loop… and puckers? Thanks so much! :wall: