Dr. Omar AbdulKafi comments on this verse saying that Ibliss promised or swore to sit in wait (to ambush) not any random son of Adam but specifically, he mentioned the straight path. When you think of it, what kind of people will he find on the straight path? Well, the people who walk on it, i.e. the righteous believers, the servants of Allah swt, the ones who perform salah and fast Ramadan and strive to do good and be better slaves. In other words, this oath that Ibliss took sounds more of a challenge where he promises to jump in the way of every believer who is attempting and aspiring to walk on Allah's path. This verse wasn't meant for the kafereen (the non-believers), those do already belong to and obey Ibliss, there is no challenge there, he wouldn't need to swear. But this is about the pious, the servants, the slaves that are striving for Allah's acceptance and blessings.
What does that mean? It means that a believer should already be prepared. A believer should know that the moment they will take their first step on Allah's path, aiming towards Allah's rewards, blessings, acceptance, mercy, etc., Shaytan will be around the corner waiting for them, to discourage them, to make them doubt themselves, to make them lose focus, to cause them temptation and distraction, trying to stop them from advancing further or to completely abandon the path. Shaytan is so sneaky that his traps don't seem satanic or evil to the believer. He will put questions in our heads, he will make us hesitate and doubt whether we washed our right hand in ablution or read a surah after fatiha or sat between the rakaat or not. But that's how he gets to you, through small thoughts in your head that you would take as your own thoughts. Then he would put inappropriate thoughts in your head when you're praying, and it only gets worse from there.
However, being aware of the traps of Shaytan is already a win for you, as now that you understand what's going on you won't be affected as much. You should also realize that you are not the only one dealing with this trial and that every other brother or sister has experienced this, at least once in their journey. The key is to always seek refuge in Allah swt from shaytan (even in the middle of your prayer, yes that's okay) and to always protect yourself by saying your athkar and doing istighfar. Also, you should know that shaytan saves his toughest traps for the strongest and most motivated believers. The harder you commit to and the farther you walk on the straight path, the more shaytan will try to distract you. That's why, you shouldn't doubt yourself or your iman, you shouldn't feel unworthy or consider yourself " a bad muslim ". Rather, keep trying, don't fall into the trap and always seek protection and guidance from Allah swt.