Because you are new, I would start simple (you can always add more!). Do the stitching around each block. If you did sashing, perhaps a wavy line down the middle of the sashing as wide as the sashing. If no sashing, then perhaps a very wide zigzag along the stitch line (more forgiving than STID for a newbie). Then, find a thread color that works for the whole quilt and stitch a line around each of the logos. If you can, you can do an echo stitch about 1/2" around. If not comfortable with it, just do a box around the logo. This will hold it, but be fairly easy for you. As you get more experience, you can try more involved quilting. A T-shirt quilt can be a very difficult thing to do - Congrats on doing it! And, remember, many 'mistakes' are simply new design elements! Think about what you created, not the small imperfections you think it has.