One thing we often see with riders doing intervals is a big spike in wattage when they start. Bam, they hit the effort and are way above target, putting themselves into deficit off the gun.
See in this effort above, it is a 2-minute effort at 261w, but the first 15-seconds are done at 316w.
Managing those spikes is a combination of gearing, the initial torque applied to the pedals and cadence. We are aiming to get towards something that looks like this.
You will want to start the effort almost on the gear that you think you will use for the interval. Then it is really a case of using a change in cadence, limiting the torque applied, to influence the wattage - a slow ramp up to the cadence you will do the interval at. As the cadence comes up the wattage increases nicely as well. There is something of a muscular feeling, but the effort is quite controlled.
Below is an interval done without that big opening wattage spike.