Your problem has nothing to do with tech skill, what you mentioned tells me that your movement is good. However, you will need to play more defensively against your training partner. Remember that even if your friend doesn't have neutral game, you still need to respect their attacks, which means that you should either foxtrot away then back, or you can use one of the best options in the game - shielding. I don't know if you have practiced power/perfect shielding, but it basically gives you a free punish on everything. Whether or not you have, just sitting in shield is very strong because even if your training partner throws out a move that you would have to respect, you can still dash forward and shield, giving you a frame advantage due to your opponent's move having some cooldown. For the fastest characters such as sheik, you may need to respect her aerials, but you will still get opportunities to punish with a nAir out of shield or even a shield grab if your opponent commits too hard, uses a grounded attack, or you read their approach. Be careful that you don't get dash grabbed or grabbed out of an empty hop though, mix up your defense by dodging or foxtrot canceling if your opponent catches on.
Another advantage that you get is the knowledge of how your partner approaches. Do they dash grab you as soon as the match starts? Do they dash attack you as you land? Once you know what your opponent will do on the aggressive, you can counter it. Remember that hitboxes will out prioritize grabs, and shielding stops dash attacks and will stop aerial approaches. There are some exceptions (e.g. Command grabs in the air) but this is generally true and you can figure out how to beat approaches for each different matchup as you go. Defensive play is very rewarding, and you can get lots of damage if you can both read your opponents approach and know Fox's, or any character's best options to punish.
That's all I can think of right now, so I hope you can use defensive play to your advantage as Fox. Keep practicing movement because it allows for mixups and can help you get the most out of whatever you do in a situation. Let me know if you need any more help, and sorry for the late reply.
I am sorry for your loss... 