Get thinner tape numbnuts.
Also for getting the lines right, what you can do is get some tape the size you want the stripe, or close to it anyway... lay that down as a mockup of the stripe, then mask around it, then remove the mockup stripe.
you can try cutting a wide strip of tape to size... but no guarantees that the sticky side will be perfectly sticky as intended. Though if it's the 3M painter's tape meant for crisp sharp lines, you might get lucky and be able to lay it down on something flat and clean, mark out the dimensions of your strip, cut it using an exacto and a straightedge or a ruler.
Also for getting the lines right, what you can do is get some tape the size you want the stripe, or close to it anyway... lay that down as a mockup of the stripe, then mask around it, then remove the mockup stripe.
you can try cutting a wide strip of tape to size... but no guarantees that the sticky side will be perfectly sticky as intended. Though if it's the 3M painter's tape meant for crisp sharp lines, you might get lucky and be able to lay it down on something flat and clean, mark out the dimensions of your strip, cut it using an exacto and a straightedge or a ruler.