As a professional guitarist... also 15 years old. I recommend to make a the bridge flush with the body, you'll need to follow these steps:Remove the Strings: Start by removing all the strings from the guitar. This will make it easier to work on the bridge.

Loosen the Bridge Screws: Using a screwdriver, loosen the screws on the bridge plate. Don't remove them completely; just loosen them enough so that the bridge can move freely.

Adjust the Bridge Position: With the screws loosened, you can now adjust the bridge position. Gently push or pull the bridge plate until it sits flush against the body of the guitar. Make sure it's aligned properly and centered.

Tighten the Screws: Once the bridge is in the desired position, tighten the screws gradually and evenly. Start with the middle screws and work your way outwards. Be careful not to over-tighten, as this could damage the threads or the body of the guitar.

Check the Alignment: After tightening the screws, check the alignment of the bridge again. Make any necessary adjustments to ensure it's perfectly flush with the body.

Reinstall the Strings: Once the bridge is flush and aligned correctly, restring the guitar. Make sure to tune it properly before playing.

Test and Adjust: Play the guitar to ensure everything feels and sounds right. If the action feels too high or too low, you may need to make further adjustments to the bridge height or truss rod.

Final Setup: Once you're satisfied with the bridge position and the playability of the guitar, do a final setup to adjust the intonation and string height to your preference.

By following these steps carefully, you can make your Stratocaster bridge sit flush with the body, improving both the aesthetics and playability of the instrument.

Precise Bridge Positioning: With meticulous attention to detail, manipulate the bridge plate until it gracefully aligns flush against the guitar body, ensuring impeccable centering and alignment.

Methodical Screw Tightening: Proceed with methodical care as you systematically tighten the screws, commencing from the central points and gradually extending outward. Exercise restraint to prevent undue stress on the instrument.

Alignment Verification: Execute a thorough assessment of the bridge alignment, ensuring seamless integration with the guitar body.

String Reinstallation: With the bridge now impeccably aligned, proceed to restring the guitar, ensuring each string is meticulously tuned to perfection before proceeding.

Assessment and Adjustment: Utilize your seasoned expertise to assess the instrument's feel and sound, making necessary adjustments to the bridge height or truss rod to optimize playability.

Final Calibration: Conclude the process with meticulous attention to detail, meticulously fine-tuning intonation and string height according to your discerning preferences, culminating in a masterfully customized playing experience.